Build Thread 200 Gallon Jungle: Notes on the SWCR Method


Community Member
Dec 19, 2022
Independence MO
The 200 gallon jungle has been a work in progress since the start of 2009. While there is a great deal to say about how I arrived at my present understanding, most of which is probably relevant but would be uncompromisingly tedious, I have no intention of treading worn ground. I can boast that what I've learned about aquatic gardening I learned on this tank build. I paid my dues in real time, failures and successes coming in equal shares for the most part. Those whose interest I manage to hold will likely have sufficient experience to track my process to the conclusions at which I arrive. I will very much appreciate questions and comments. It is not possible to lay the whole scheme out in one go, so this post is only a starting place. I plead your patience; all will be revealed.

While this aquarium is certainly of the high-light/high-tech school (hereafter HLHT), the original, really meaningful influence on my thinking about planted aquariums was - and is still - Diana Walstad's Ecology of the Planted Aquarium 1999 [2nd Ed 2003]. Walstad is a proponent of the natural method, and the aquaristics she promulgates are not wholly consistent with HLHT practices, to say the least. But those ideas are at the core of what aquatic plants and their culture are all about. That is where the basic science begins. From Walstad I went to my limnology, ecology, and environmental engineering textbooks with a whole new lens through which to look at this, and that is what sparked my serious interest in this hobby.

The "jungle style" is a category most akin perhaps to Amano Nature. It verges on Dutch style but eschews the "formal garden" discipline. It is decidedly not diorama, but could share certain features with it. The jungle style's defining characteristic is that it is wild. It looks like an assemblage of opportunistic plants competing for space and light, because that is essentially what it is. Given space restrictions, certain rules do apply. Tall plants at the back, less tall plants at the front. Density is a key feature, but congestion is unhealthy; it takes some practice to get that one right. A first principle in the philosophy of the jungle style is to give the ecosystem freedom to express itself. Give plants their head. They go where they go for a reason. The aquarist should not interfere until necessity dictates. A lotus volunteer pops up in the foreground, which is the last place you'd ordinarily plant it, but that's interesting. Seeing that is why I do this. Life making its way is a profound thing. If I create a world where nature is happening, that's gratifying beyond words.

These are pics of the jungle today. I have been rescaping and pruning, and am in the middle of some larger maintenance procedures a bit overdue. So this tank is not looking its best just now.




SWCR is Streaming Water Change Regimen. This is a method I have been experimenting with for the past two years and am confident now that I have proof of concept as to its utility. It necessarily requires a high degree of automation in system functions, especially supplement auto-dosing. I will describe it in detail, but I do not necessarily advocate it. It's definitely not for everybody. Neptune Systems Apex makes this method possible.
Nice write up and interesting unique tank.

I am curious what do you consider high light? Any idea of the PAR at substrate?

And what is the high tech aspect of the tank? Is it running CO2?

Just trying to get a better idea of and learn more about all that is going on in there.
Yes, this is a true HTHL setup. I will be getting more thorough with the details. I am using CO2. Apex controls pH at a constant 6.74, running total average. Buffer is auto-dosed to maintain dKH at 6.5 - 7. CO2 is thus regulated at 30 - 40 ppm.

I do not continuously monitor PAR and haven't dropped the sensor in for some time. I use Kessil LEDs. Seven (soon to be nine) A80 Tuna Suns and three A360 Tuna Suns along with 24 feet of magenta/white strips. It's a lot of light. Over time I have adjusted intensities to maximize brightness and minimize algae-inducing over-illumination. Having arrived at the lighting that seems to work best, I haven't been concerned with an actual number. Now I'm curious, so perhaps I'll get a PAR number soon.

I will be describing the lighting and CO2 systems thoroughly, with schematics. It will take a few posts to fully describe this system.
I paid my dues in real time, failures and successes coming in equal shares for the most part.
Love this. Very well said!
Life making its way is a profound thing. If I create a world where nature is happening, that's gratifying beyond words.
WOW - I am so enjoying your prose!
SWCR is Streaming Water Change Regimen. This is a method I have been experimenting with for the past two years and am confident now that I have proof of concept as to its utility. It necessarily requires a high degree of automation in system functions, especially supplement auto-dosing. I will describe it in detail, but I do not necessarily advocate it. It's definitely not for everybody. Neptune Systems Apex makes this method possible.
OK so as a tech guy with an Apex, I'm really looking forward to reading more about this.

I'm a Kessil guy as well and want to see more about the lighting and what you've found with such a large tank.

On your style, jungle, of course, is a good way to describe it but, at least to me, it doesn't capture the hidden beauty and order to it. The Japanese use the words Wabi-Sabi to describe the beauty in the imperfection. To me, that is what I'm appreciating about your aquascape. It's beautiful in the way you allow nature to find its way with only light ordering from you as needed.

Looking forward to reading more! Thank you so much for posting this.

Oh, and you may want to create a banner under your name that links to this, your build thread. Here are the instructions on how to do that: Build Thread.
Certainly Wabi-Sabi is apt. The effect sought is the shoal margin of the littoral zone of a rain-forest primary stream.

A subtitle for this thread might be Apex Aquacontroller Applications in Planted Freshwater Aquaria. Changes are coming to this tank's circulation and support systems in the spring so there will be some revisions. Of course, there are always pending revisions aren't there? But to give you the idea of the scope of this, here are screenshots of the dashboard.



The SWCR is actually a water change protocol performed in batches - quanta if you will - as a means of simulating a continuous throughput of water from "upstream" to "downstream". This method utilizes Apex timer functions to meter each quantum uniformly on a schedule (in this case hourly). Each quantum is released from the system by a solenoid valve going to drain. This is an Open Drain Event, ODE. By experimentation, the volume of water drained in the programmed ODE is predetermined. Currently, the ODE time is exactly 3 minutes and drains about 4 liters of tank water (I need to recalibrate this, as it might be off a bit). Supplement dosing is programmed to occur daily before sunrise just after the 06:00 ODE. No further ODEs occur during daytime until 15:00. The total daily demand on the RO/DI sourcewater system is 64 liters (17 gallons). The following program is how Apex does this.



The SWCR removes autochthonous product of environmental metabolism in quanta. As it also dilutes supplements in like manner, it is necessary to calibrate the dosing levels of all additives accordingly. This is also fully automated. Once the system is performing on balance, the background water chemistry and macrophyte nutrient concentrations are maintained automatically, stable within prescribed tolerances. This is why frequent testing is needed; dosing calibration depends on determination of the maintenance of all parameters. The dose rates are metered not by varying solution concentrations but by adjusting the run time of their respective peristaltic pumps. The fertilization and hardness reconstitution are controlled entirely by modifying timer programming for each parameter independently. This automation not only assures rigid time and quantity regulation, but confers total control of water chemistry on the aquarist entirely by means of very simple program line rewrites.

The SWCR will have the cumulative effect of diluting the water column at a constant rate such that in just a few days it will be clear that the aquarist can readily manipulate the trophic status of the habitat. The specific latency of the effect will depend on volume and scheduling of the ODEs and the corresponding supplement dosing. Frequent testing is crucial.

There are questions about the dosing scheme and testing. I will address these in detail coming up.

I hope everyone's tanks will make it through the storm okay.
So, I need to read your explanation a couple of more times before I can digest it. It seems to me that you are simulating a nursery style runway system that is used by aquatic plant growers in high-tech nurseries.

Water moves in one direction in the runways where aquatic plants are growing. Daily water changes happen to keep it like an open system. Nutrients are added by computer to maintain a stable level.

You seem to have adapted this to the home aquarium. I think but I can be completely wrong. I need to re-read your post. For me, @Graham, pictures are very necessary. I'm a visual learner. Got any of the actual system? I appreciate the Apex and will likely be asking you questions about it for my setup.

I think Apex and Apex-like computer systems will be helping us with our aquariums as THE standard in the future.
In this case, hourly "water changes happen to keep it like an open system." The experiment began with wondering how to create a true continuous slow water change. This was not really practical to implement because of uncertainty in flow rates. It looked like something that would be difficult to manage from a technological point of view. However, doing a 4 liter water change on the hour is a cinch, and just as good. It is necessary that the ODE be sufficient to draw the waterline down just far enough to trigger the ATO at least. Beyond that, the ODE can be set for a duration that will drain a target volume. The point of connection of the drain solenoid is from a post-pump filtration loop. Drainage is channeled away to house D-W-V. I measured the volume of discard that would cause the ATO to start with the circulation system running (normal pressure). This turned out to be 3.375 liters. I then programmed the ODE time for a 4 liter discard. This turned out to be approximately 3 minutes. This is the sort of thing Apex does very well. Thus, the "continuous" water change is actually done in batches. I can shorten or lengthen the ODE, i.e. I can size the quantum, by altering the timers in Apex.

It is also possible, of course, to program for any number of ODEs in a day. I interrupt the hourly routine between 06:00 and 15:00 to stop water column dilution after supplement dosing so the plants get full benefit early in the photoperiod. Nutrients and hardness reconstitution are added by computer. The objective is to keep target values within desired ranges at all times. Apex is programmed to run the dosing system so as to promote compensation of each parameter in response to the SWCR (and, of course, plant utilization). This is artificial homeostasis. The dosing rates are determined by experimentation so as to yield the necessary equilibrations. The dosing pump timers are programmed to deliver accordingly. Thus, the apparent homeostasis is strictly predictive as there is no actual auto-feedback loop. The aquarist's tests are the feedback loop. (An example of a true homeostatic system is the metering of CO2 by means of pH controller.)

I have found that I tinker quite a bit with the dosing timers. After a few days this or that parameter looks to be drifting so some fine-tuning adjustments are done. There was a time when I thought I might be able to reach an ideal state of artificial homeostasis by fine-tuning the system wherein very little or no adjustment was necessary. That particular objective was not to be realized. However, Apex has gotten me next best. It is possible to amend supplement delivery by simply changing the dosing pump timers. After awhile the system is tuned fairly well and values stay relatively stable. In event of drift or changes, it is a simple matter of altering a program line. Fertilization in this system does not involve formulae or resets. Each supplement (fertilizer or hardness recon) is dosed according to need. Each dose is administered in equal amount at the same time daily.

This is the auto-dosing system.

This is the auto-dosing system
Are those Magnetic Stirrers the bottles are sitting on? If so do they come on a minute or so before the dosing pump energizes?
Edit: I have an IAqua control board and all the electrical components but have never taken the time to set it all up...
The stirrers are Hanna Instruments 190M (120 VAC). The dosing vats are AquaMaxx DC-1 (1.5 liter). The peristaltic pumps are Milwaukee Instruments MP810 (10 mL/min, 120 VAC). The stirrers are ON about 1 minute before the first doser ON, then OFF when last doser OFF. I will be adding an eighth doser to handle organics/botanicals additives. The stirrers help with solutions that tend to settle, but not with substances that have poor solubility such as CaSO4. These will clog the lines.
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The 200 Gallon Jungle is meant to be a simulation of the littoral zone of a tropical rain forest primary stream. Taken as a whole with all its support systems, the aquarium contains living organisms, obliging us to understand it as a processing facility. The aquarium necessarily resembles both these things. The real natural habitat being simulated is an open system. Each parcel of ecosystem is contiguous with the parcels immediately upstream and downstream from it, the whole local-regional interconnectedness ultimately spreading to the entire biosphere. By contrast, the aquarium is a carve-out parcel. It is a glass box. No matter what its size or how elaborate its infrastructure, the aquarium is a closed system. I think the essence of this enterprise is to visualize a beautiful living microcosm, and to realize that the whole thing is, in fact, a wastewater-water treatment plant. The key to achieving the former is in the implementation of the latter. This is the art and science of aquaristics.

Soluble product classified according to source is allochthonous or autochthonous. Autochthonous product is that generated by the ecosystem internally by energy extraction from breaking of molecular bonds. Food (complex organics) passes through a complex and interdependent chain wherein all living participants eventually process every bio-labile substance, fully mineralizing it or assimilating it (environmental or community metabolism). Allochthonous product is that which is imported into the ecosystem from adjacent sectors, generally organics like humus and related complex organics from contact with terrestrial litter and inorganics from contact with exposed native rock. Autochthonous dissolved inorganic nitrogen (DIN) incudes ammonia/ammonium, nitrite, and nitrate which is derived from any nitrogenous source present, but particularly from heterotrophic decomposition of dissolved organic nitrogen (DON) such as urea and proteinaceous precursors (decomposing into peptides, amino acids). Allochthonous DIN includes all such soluble product that is present in water that flows into the ecosystem via runoff and percolation, and, in the aquarium, that which is deliberately added by the aquarist such as nitrate salts used as plant fertilizer. Nitrate in the aquarium will likely be both derived from fish food (autochthonous) and dosed as an inorganic additive (allochthonous). Orthophosphate will similarly have allochthonous and autochthonous sources in the planted aquarium.

Natural bodies of water are classified by trophic status which relates directly to degree of fertility favoring aquatic plant life. Oligotrophy is defined as the trophic state wherein DIN is less than 10 ppm and orthophosphate is less than 2 ppm. Eutrophy is defined as the trophic state wherein DIN is greater than 30 ppm and orthophosphate is greater than 5 ppm. Mesotrophy is defined as the trophic state wherein DIN is 10 - 30 ppm and orthophosphate is 2 - 5 ppm. These states arise from the respective nature and abundances of their ultimate food sources and corresponding rate of autochthonous product generated by their environmental metabolism. Oligotrophy will typically have the lowest concentration of organically bound phosphorus, 4 - 10 ppm, and other dissolved organic carbon (DOC, or dissolved organic matter, DOM) waste in various states of decomposition. Eutrophy will typically have the highest concentration of organically bound phosphorus, greater than 35 ppm, and other DOM. Mesotrophy, again, is intermediate. The DOM supports heterotrophic metabolism so is measured by, and is synonymous with, the ecosystem's biochemical oxygen demand (BOD). Other things being equal, particularly the oxygenation profile of the habitat, the redox (oxidation-reduction potential, ORP) corresponds to the BOD, and is a good indicator of DOM in the ecosystem. So typically, for the same O2 tension, ORP will be somewhat higher in oligotrophy than in eutrophy. As would be expected, aquatic plants in general are favored by more fertile waters, so are sparse in oligotrophic conditions and abundant in eutrophic conditions. Algae, notoriously, associate with eutrophy.

So where do our aquariums fall in these categorizations? Quite simply, our nitrate and phosphate test kits tell us that. What values should these and other parameters have for a successful planted aquarium?

The SWCR is an effort toward reproducing nature's openness by the expedient of water changes using RO/DI to replace nutrient loaded water. As in a primary stream, this is exportation of autochthonous product downstream, with purer water flowing in from upstream. The trophic status of this ecosystem depends on the rate of evolution of the autochthonous nutrient load and its dwell time, or rate of throughput of the solvent stream. These factors can be controlled by setting the rate of water change (size and frequency of open drain events, ODEs), and dosing rate of allochthonous supplements. With SWCR utilizing RO/DI water, it is possible to actually "dial in" the trophic status of the ecosystem. While it's not a truly open system, it's starting to look like one.

The aquarium water is continuously circulated through filter apparatus. Part of the filtration process is commonly chemical uptake of DOM by various means and materials. I have alternately run pro and con on chemical filtration for as long as I've been doing this. The SWCR is a far superior means of exporting DOM. The ORP in the Jungle is extremely high. Chemical filtration media may have its uses in certain situations, but in a big tank it is not inexpensive. I think keeping the RO/DI system in top working order is a better investment. Not using chemical filtration media also short-circuits entirely the question as to its possible downsides such as removal of desirable substances. Also, with SWCR and auto-dosing inputs and outputs are effectively metered with predictable results. I've always been uncertain about media, how much to use, and when to change it. There's nothing quite like a water change, especially if you can do it with just valves and pumps!

The SWCR necessarily requires frequent testing of every important parameter. Here is the testing protocol for the Jungle.


Approximations for macronutrients NO3 and K are appropriate for assessing adequacy in a mesotrophic habitat. My NO3 currently tests at 13-18 ppm. This is a dip-and-read test strip. It's as accurate as any other test kit I have used measuring in this range, and it's much easier. Do I care if NO3 is 12 ppm or 20 ppm? I don't. Both values represent sufficient nitrogen, and likely allow for luxury uptake, so there is no good reason to pin down this number more precisely. The potassium test is based on light transmittance through turbidity and can easily be read out to within 5 ppm. It too is a very easy test to perform. My K routinely tests at 40 ppm. Do I care if K is 35 ppm or 45 ppm? It doesn't matter. Measuring the concentration of a nutrient that is provided in luxury uptake scale, it is not necessary to be precise; it is good to be easy. Phosphate usually tests under 2.50 ppm. In this range for PO4 precision is both desirable and possible.
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Today's numbers

pH: 6.76
ORP: 535 mV
TDS: 340 ppm
NO3: 17 - 22 ppm
PO4: 2.50 ppm
K: 40 ppm
Fe: 0.67 ppm
dGH: 3.6
Ca: 16 ppm
Mg: 5.9 ppm
Ca/Mg: 2.7
dKH: 6.7

The answer to the question "What should these values be?" is these numbers. This is a mesotrophic soft-water ecosystem. N : P : K = 9 : 1 : 16. This is where I want the Jungle to be.

The last year in this experiment has been instructive. I set the parameters to maintain oligotrophy to test the idea of a low-nutrient system. Nitrate and phosphate were kept at levels supported by only autochthonous product with very little or no allochthonous input. A working hypothesis under test was whether plants would prosper in low NO3 and PO4 as long as these nutrients were non-zero. Fish were fed very generously with all types of food and tests for NO3 and PO4 were typically very low but non-zero. I did not depress potassium concentration, but the system was otherwise kept in super-oligotrophy. I did push fertilizer tabs, both micro and macro, into the substrate around the swordplants, but I can't honestly say I drew any useful conclusions from doing that.

The carbon and light supply were kept up and O2 levels showed the plants were fixing carbon. However, despite this the plants stopped growing. At the point where nuisance algae began to appear this experiment was halted. I immediately started pumping nitrate into the tank. The system is now mesotrophic and is recovering nicely. Plants are growing again and regaining color. I am getting on top of the algae situation. Two years ago this tank was operated in mesotrophy and was healthy and vibrant. I am getting back to that as quickly as possible.

Robust plants and lots of them are the answer to algae.
Have you seen that the substrate is soaking up some of the nutrients? How about plant consumption per day? I would think these would show themselves easily in this system.
If the nutrient dose allows for luxury uptake this means that ionic concentration in the water column is sufficient for the plant to take in all it needs and all it can store. The plant is literally awash in fertilizer. To the extent that a plant can uptake any nutrient through leaves and stems (foliar uptake) it will have unlimited access to this plethora.

The substrate is inert rounded grain 1 - 4 mm ("coarse sand" to "granular pebble" on the Wentworth scale) washed alluvium composed of plutonic clastics quartz and feldspar (the micas and amphiboles long since mostly pulverized and shed); it's what is sold as "natural" aquarium gravel. These clastics are insoluble and chemically inert and have no cation exchange capacity (CEC). I amended this gravel with equal part SeaChem Flourite which is a fracted clay and possesses some CEC. Also a good-sized portion of granulated laterite was added. I elected to not go with specialty fertile substrate materials. This substrate is stable from start to forever. That is a variable avoided. Age brings incorporation of mulm over time in a biologically active environment so there is deposition of organics. Water does not circulate in the substrate, so ions move by simple diffusion only. Roots can, I think, get at nutrient in the water column. So, yes, the substrate in effect soaks it up, thus extending the plethora to the rhizozone.

The plants will take what they need without limit, and in the mesotrophic habitat the nutrient is unlimited. So the actual fraction of the available ions that they consume in a day is not meaningful information (in the sense of being useful). The SWCR removes allochthonous nutrient systematically, so the portion of the draw-down attributable to the water changes and the portion attributable to consumption by the plants cannot be parsed. It should be clear, however, that as the point of auto-dosing is to compensate the SWCR, the values of the parameters should remain stable. Allochthonous supplementation prevents downward drift of nutrient due to increased plant growth, which would lead to deficiencies, while the SWCR avoids unnecessary excesses and exports surplus DOM. I know this balance is operating in the Jungle because I test. And I am able to tune this balance on the keyboard I am using to write this post. The numbers listed in the above post are actual test results from this morning. The next time I do tests, I will get identical or similar numbers. And if I detect drift I will alter the appropriate program.

The NO3 and K are dosed for plethora. I think the larger part of PO4 in this system derives from environmental metabolism of autochthonous product, with just a small daily shot of KH2PO4 supplement. Carbon availability being high, the plants are not growth limited and are controlling the PO4 concentration. Orthophosphate is not high even in mesotrophic systems, so if I'm taking nature's example I do want it limited. The redox is very high so probably the BOD is very low. To the extent that algae is favored by any excesses in PO4 and DOM I think I am doing what is possible to thwart it. Healthy happy plants are doing this work. Now that they are growing again the habitat is slowly evolving out of its nuisance algae problem.
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@Graham you're blowing my mind here with the eye-candy and details. I feel like I need to print this thread out and read it like a magazine (I'm old, ok?).

Given the holidays and family at my house, I don't have the time to thoroughly read this. I hope to in a few days. Keep the info coming!
I’ve done several continuous water change systems, eg slow dripping or a small pump sending wastewater to the drain and a float valve to refill. These work fairly well but nothing beats a large 50-90% water change for the plants themselves. I have an automated system for the two tanks I am redoing based on the small daily changes, but the system has a semi manual that uses a valve and U shaped pvc siphon to drain to whatever depth I choose. The wastewater goes into the same drain pipe as the automated water change drain. There’s a barbed end I can use for a gravel vac also should I need one. Small water changes seem to work best on ferny mossy grassy low to moderate lit tanks. The high light stem tanks, less so. Still, they work BETTER than manual systems which often get neglected no matter who you are. We ALL slack off or go on vacation for 2-3 weeks and come back to a mess. There is not a need for proof of concept nor getting too picky with the auto dosing. Tap water prep, activated carbon typically is all that is needed. If you want a soft water tank and have higher kh, RO for your float water source then. I always over sized the RO units. Hope this helps



The Nymphaea lotus on the left end of the tank is coming in very fast. Once they get started they are prolific. In three days it has sent up two floaters. It is also producing numerous arrowhead midwater leaves and has sent out runners to foreground sites where leaves are popping up. This may be a 'rubra' as was my avatar, but I can't be sure until it blooms. If I let it produce floaters, which throw a lot of shade, it will bloom this year. The N lotus bulb I planted on the right end of the tank is not producing. It is set back in among the swords and Java ferns and I suspect it's too dark in there. It may yet do something someday and I'll be in for a nice surprise. These plants get big and are perfect for a jungle type 'scape.

The Echinodorus 'oriental' are all putting out flower spikes and there are usually new plants on the nodes. I find this interesting and wonderful. Too much of this is a little unsightly, but I will let the best-looking ones go on for awhile. I have four E 'oriental' in this tank, and one E 'ozelot'. The ozelot has never sent out a flower spike. Kasselmann states "adventitious plants on inflorescences is rarely observed in the aquarium." * I have had this ozelot for at least five years and I can confirm this.

There is a stand of Echinodorus grisebachii 'Tropica' growing in the left foreground. When I first set the newly acquired mother plant it had a small but well-developed inflorescence with several tiny daughters. I bent this down and tossed some gravel over it. They all established and are coming along nicely. I am delighted with the vitality of the Cryptocoryne wendtii. All these plants in the foreground are volunteers from runners produced by the larger Crypts in the midground. They are tolerating this light very well and are growing fast.

I pruned the Hygrophyla difformis and netted out debris just before these pics were taken. H difformis goes up and spreads out under the light and it impedes the surface currents. There's always a lot of Hygro fragments when I top these plants. Today I will return the gyre pumps. These are good at gathering debris. I routinely remove them for a day's bleach soak. Although this is a maintenance chore, I like that they seem to be effective surface skimmers. They are excellent at moving water through the big leaves in the Jungle.

*Kasselmann, Christel: Aquarium Plants, 4th Edition, 2020.
Probably should dilute the tank by 2-3x and up the CO2 about 10-15 ppm base on pHKH. Adding more algae eaters etc

Today's numbers

pH: 6.75
ORP: 539 mV
TDS: 340 ppm
NO3: 22 ppm
PO4: 2.12 ppm
K: 35 ppm
Fe: 0.65 ppm
dGH: 3.4
Ca: 16 ppm
Mg: 4.9 ppm
Ca/Mg: 3.3
dKH: 6.5
CO2 > 30 ppm
not sure your testing methods or if there are standard references that you use, but the tank does do fine assuming they are correct but the plants could do just fine with 1/2 these amounts. CO2 could be bumped up to 40-45 ppm and more algae eaters and shrimp would help. This would improve growth and make the tank more resilient. ORP is not 530-540. Something is wrong with the probe. 400 ish mv would/should be the maximum. Stray current or some other factor might be influencing it and likely the pH probe if so. This will make you believe you have a higher CO2 level than you think. The GH seems a bit low given the KH. Often times that is due to a tap water water softener adding salts. Ideally for plants you’d want the reverse, low KH and higher GH.
The Apex ORP has always returned high numbers. Probably if I calibrated it it would give more realistic numbers. The Pinpoint monitor shows around 450 mV; it probably needs calibration, but I believe it's in the ballpark. As an absolute value of 400 or better, I will take this as high redox in any case. Apart from that I am more interested in change; as long as the system is consistent it will report movement. This tank water has redundant earth grounds, so I do not suspect electrical disturbance. I have three pH monitor probes in this tank and they are all calibrated. They are verified accurate.

CO2 in this system is usually closer to 35 ppm as I deliberately keep KH around 7 degrees. If I push the pH down to 6.7 I could do better still. Not averse to the idea of increasing CO2, but I am getting good growth with the 30 ppm floor. You perhaps are accustomed to lower KH and pushing the CO2 so the pH is quite low. I prefer to use alkalinity to adjust the CO2 because I prefer not to operate my aquarium below pH 6.7. What organisms are experiencing in their environment that is chemically significant is pH. KH by itself is just a number, it's essentially a figure of merit for a carbonate buffer system.

There is no natural relationship between GH and KH in this tank. The SWCR systematically removes buffer. This is why potassium is dosed as K2CO3. The primary source of added buffer is CO3. The auto-doser is calibrated to maintain a specific KH at the SWCR dilution rate. This also keeps K in luxury uptake territory. The GH is held to a value where the Ca and Mg ionic concentrations are not limiting to plants (or at least any that I'm currently trying to grow). Not being excessive, this provides a reasonably soft soft-water habitat for the tetras. You state that "Ideally for plants you'd want the reverse, low KH and higher GH." I know in "ordinary" circumstances the KH and GH numbers are the inverse of this. I see no reason to regard this as doctrine and I require evidence.

Just for clarity, I use RO/DI sourcewater. I do not use tap water.

What parameters specifically should I halve and why? What do you mean by "should dilute the tank by 2-3x?" I am keeping orthophosphate below 2.50 ppm. I would prefer it a little lower but I'm not obsessing. Potassium is not toxic at 40 ppm and I will never have cause to suspect a deficiency. I have elevated NO3 from 5 ppm, which was trouble brewing, to 20 ppm, which got me out of trouble. I am not looking to go much over 20 ppm. Iron is tested within two hours of the AM micronutrient dosing.