Resource Rocco's Nutrient Accumulation Calculator

[Naturescapes_Rocco]

Running a tank with BDBS (inert sand substrate), no root tabs, no aquasoil, and only dosing DIY ferts via EI/"non-limiting" methods has been extremely enlightening (and successful!). To help my journey, I created a tool to help myself and others who use weekly water changes and manual fert dosing:

Rocco's Nutrient Accumulation Calculator​

Journal for this tank is here!​

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Who is this calculator for?​

For anyone dosing fertilizers into their water column, especially for high-energy (high light, high CO2) tanks that require large doses. It's especially helpful for tanks with inert substrates but high energy, such as inert sand/gravel tanks, because aquasoil both absorbs/releases/messes with water column nutrients!

Why does this calculator exist? Aren't there other similar calculators?​

Rotala Butterfly has a nutrient accumulation calculator, but it's nowhere near as customizeable/adjustable as this one! This calculator exists to cover nearly every possible option for water column dosing -- daily dosing, once-weekly front loading, split doses, and everything in between.

How do I access it?​

Make sure you're logged into your Google account, and in the calculator, go to File > Make a Copy! You can also use File > Download to open in Excel if you prefer, or don't have a google account.

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Let me know what questions you have!​

 

[Naturescapes_Rocco]

An example for tanks with large (60%+) weekly water changes:​

After years of trial and error, lots of research, and building a high energy tank around high-light, high-CO2 and high plant growth via dry fert dosing, I know that I'm interested in maintaining ~30ppm NO3 in the water column per week. I change 70% of my tank's water on Sunday evening. I test/estimate that my plants consume between 2.5-3.5ppm NO3 per day.

Option 1: I can "Front Load" my 30ppm KNO3 dose once each week after the water change. My results would look like this:

30ppm, front-loaded in one dose after the weekly 70% Water change
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Notice that the levels fluctuate ~18ppm in weekly max difference. Plants like consistency almost more than anything else, so while this works, we can improve on it!

Option 2: to improve the fluctuating levels, I can split the 30ppm dose into twice-weekly 15ppm doses, one on Sunday after the water change, and one on Thursday morning:

30ppm, split into two equal 15ppm doses through the week
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Notice that the levels fluctuate less than front loading, AND the maximum ppm in the water column is almost 1/3rd less. But can we do better?

Option 3: A 20ppm "double dose" after the WC, with one 10ppm "single" dose halfway through the week:

30ppm, split into one large 20ppm dose after WC, and one smaller 10ppm dose midweek
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That's more like it! More consistent, less swings.

What about daily dosing in a tank with 70% Water Changes?​

Option 1: Let's say I have a Chihiros Auto Doser (which I do!) and I want to use it to dose 30ppm per week into my tank via daily dosing. That would be ~4.3ppm per day:

30ppm, split into seven daily 4.3ppm doses, with a 70% Water Change
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Nice! That's pretty damn consistent. Lower water column nutrients would increase the reds/colors of many plants, potentially reduce Green Dust Algae, but might run the risk of bottoming-out (reaching zero ppm), which could trigger algae growth if plants are stopped from growing due to no NO3.

Option 2: But wait! What if I use the Chihiros app to partially "front load" some of the weekly dose after the water change, then let the daily doser do it's thing with a slightly smaller daily dose?

30ppm, split into one 6ppm "recovery" dose post-WC, then daily 3.5ppm doses, with a 70% Water Change each week
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Only a 3.0ppm max difference through the week? That's about as consistent as it gets! Though, that's dependent on a steady 3.0ppm daily uptake, AND requires your dosers to be not only accurate, but reliably used every single day. If your auto doser fails, you're screwed. Plus, it still requires some manual effort for that "recovery" dose after the WC.

But, in a perfect world, I think this is my dream setup.

A non-daily-dosing example for tanks with smaller (35%) weekly water changes:​

30ppm front-loaded after a 35% water change will eventually reach high levels of accumulation.
Larger water changes do make this easier to manage!
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Since I'm not removing as much excess NO3 via water changes, I need to dose less:

20ppm front-loaded after a 35% water change. I also reduced the "Daily PPM Uptake" to 2.0ppm/day. This could be done via reducing light intensity primarily, or water temperature secondarily.​

What system do I use and why?​

Well, I've been trying all sorts of dosing systems for the last few years! If you want to know, please ask me via comments so I can provide the latest updated system I'm using.

Currently, I've had great success with dosing my macros 30-9-39 with a 70% WC, twice weekly, with a large front-loaded "initial" dose after the WC and a smaller "booster" dose halfway through the week.
That's adding 30ppm NO3, 9ppm PO4, and 39ppm K manually per week.
The post-WC recovery dose is 20-6-26, and the booster dose is 10-3-13.

I do this because I find that a single front-loaded dose after the weekly WC? Easy!
Adding a second dose midweek? I might forget, but I don't mind too much and it's helpful to keep levels consistent.

Dosing my tank 3 time a week? That's too much effort/memory/reminder required.
Daily dosing via my auto doser? I'm curious about trying it again, with a slightly larger "recovery" dose for sure. However, that relies on these cheap chinese dosers functioning both accurately and properly over long periods of time. Calibration with Chihiros auto dosers is actually super easy so I don't mind re-calibrating every 2-3 months, but they just don't feel reliable enough for me to try it... yet!

 

[Rob23]

@Naturescapes_Rocco This is great! Thank you for the detailed write-up.

I test/estimate that my plants consume between 2.5-3.5ppm NO3 per day.

Can you expound on this a bit? How are you getting that level of precision with the Salifert nitrate test? Given your recovery dose is 20ppm, I would think that puts you into the 25ppm level on the kit's chart. From there the chart drops to 10ppm. Are you diluting your sample to help with your test/estimate?

 

[Sb1415]

awesome post as usual.

When you say you dose 30 ppm of nitrate per week, is that 30 ppm/ml or the ml needed to rise your tank volume to 30 ppm ?

 

[Naturescapes_Rocco]

awesome post as usual.

When you say you dose 30 ppm of nitrate per week, is that 30 ppm/ml or the ml needed to rise your tank volume to 30 ppm ?

That's however many grams of KNO3 I need to add to raise the total weekly dose to 30ppm:



6.3g KNO3, in 34 gallons of water, is 30ppm added per week.

4.2g added after WC, and 2.1g added halfway through the week as a booster dose.

 

[Naturescapes_Rocco]

Can you expound on this a bit? How are you getting that level of precision with the Salifert nitrate test?

It's a little bit of everything! Testing, estimation, comparisons to other well-tested users/journals.
The easiest way is to do 1 week of front-loaded macros, and test at the beginning and end of the week. That gives you the weekly consumption.
This tank (and my big tank) have similar PAR levels now, and since they're both HEAVILY planted, I also see similar levels.

I've also seen journals from other legends like Gregg and Burr who have posted about levels of consumption in high-tech planted tanks.

My testing has shown between 2.5ppm and 3.5ppm NO3 per day; that helps me know a rough estimate. The IMPORTANT part is that exact levels don't matter with 'EI' dosing -- as long as you never bottom out, or go into crazy excess, you're good!

Given your recovery dose is 20ppm, I would think that puts you into the 25ppm level on the kit's chart. From there the chart drops to 10ppm. Are you diluting your sample to help with your test/estimate?

Yes, diluting 1/2 with pure RO water and multiplying the result by 2 is the best way to do it. I do the same with the salifert PO4 kit.

That's partly the beauty of BDBS inert sand; I know exactly what I have and what I don't have, and can adjust accordingly.
In an aquasoil tank? Testing NO3 in the water column might not be as useful information, since there is some amount of N stored in the aquasoil itself. Like @GreggZ said,

Over the years I have had tanks with both BDBS and aquasoil. You can have a great tank with either. In the end for me it was just easier long term with BDBS. I can control every single thing and I like that. No surprises, and no fighting aquasoil as it changes over time.

I'd like to create a resource for posting commonly-tested daily consumption levels in high-energy tanks.

What I've found so far from my own testing and research so far regarding water column uptake in high-energy tanks:

• NO3 is consumed somewhere between 2-4ppm per day in most cases
• PO4 is consumed at a ppm rate of 0.2-0.5ppm, usually 1/10th NO3, but can sometimes be consumed faster than 0.1x
• K? Not sure. @Burr740 talks a lot about how K is similar to Ca and Mg, where they need to be present in "X" consistent levels, but aren't actually consumed that much. I've tested that the K in my tanks is usually consumed between 1x and 0.5x the NO3 per week or less, so between 1-2ppm per day? I could be wrong.
• Ca isn't consumed much, but needs to be present in some amount. Maybe 0.1ppm per day, potentially more or less? I don't have a test kit, but have seen great results dosing 20-30ppm Ca in general (RO water).
• Mg isn't consumed much... more than Ca, but less than K. Maybe similar in rates to PO4? Again, I don't have a test kit, but other legends have done testing and researched more than I have and say that Mg isn't consumed that rapidly, it just needs to be present again like Ca. 0.1-0.3ppm per day?
• Fe isn't consumed much at all, maybe 0.01ppm per day in some cases. I won't speak much to this, because I'm likely completely wrong, and I know so little about micros (but I'm learning as I go now!).

EDIT:

In this post, Burr talks about getting ICP tests done through the week on a high-energy tank:

I had icp tests done a few years ago, t post water change, mid week and end of week, on 3 different tanks. Ca barely moved, K only dropped 3-5 ppm. Both were front loaded post water change (all at once for the entire week)

Just a bit more info on this subject!

 

[Gwad]

@Naturescapes_Rocco great calculator! Thanks for sharing.

I've found for my overly stimulated and tired brain that daily dosing is easier for me to remember to do consistently than any 2 or 3 times per week schedules. After seeing your results here, I will probably start doing a double dose on water change day to make it even more stable.

 

[Burr740]

The "need to be present" in regards to Ca and Mg specifically, and to a lesser degree K, has a lot to do witjh plants tendency to strive for an ionic balance internally, with a slight lean to the negative. Its all passive and depends on what could be described as pressure within the plant vs without (in the water column) Example even the highest energy tank packed with fast growing stems might only pull 1 or 2 ppm Ca per week. But good luck trying to run a tank with 1 ppm Ca in the water. It just doesnt work like that

 

[Sb1415]

That's adding 30ppm NO3, 9ppm PO4, and 39ppm K manually per week.
The post-WC recovery dose is 20-6-26, and the booster dose is 10-3-13.

Looking at Rotala butterfly and trying to calculate the result of my dose. I see that the website displays No3 ppm and N ppm differently while I had always used it interchangeably especially when quoting NPK.

The calculation for Conversion is

• 1 ppm NO₃ → 0.226 ppm N
• 1 ppm N → 4.43 ppm NO₃

In your ratio for NPK do you mean N or No3 ?

 

[Naturescapes_Rocco]

I mean NO3 for sure!

90% of all ferts use NO3 as the source of N. Also, test kits are for NO3, too.

The dry salt I use is KNO3. Same for KH2PO4, where I’m adding P as PO4.

So if I (and most other hobbyists) list my dose as 30-9-39, that's 30ppm NO3, 9ppm PO4, and 39 K total added per week.

 

[ScaperHaynes]

@Naturescapes_Rocco Any suggestions on how to account for "extra" water changes in a week with this methodology?

For example, this week I did an additional 50% water change to combat some fuzzy white stuff that won't stop growing on my mylasian driftwood (seems to be fungus according to Dennis Wong's site, and should go away eventually). Not to mention, I had a little plant melt this week after finally getting a diffuser clip for the Photone app and discovering my lights were at 250 PAR on the substrate. (Adjusted them to appropriate levels of course).

I thought it seemed logical to dose the water used for replacement to theoretically match the dosage levels in the tank at that point in the week per my standard dosage and water change schedule. That's what I did, and I'm sure this isn't totally wrong but was curious to see how you'd approach this type of situation.

 

[Naturescapes_Rocco]

I'd say that makes sense!

Elements like Ca or Mg don't get consumed much at all, so will always eventually approach whatever the max is no matter how many water changes you do. K is also a bit like this, but definitely gets consumed faster than Ca and Mg both, but not as much as NO3 or PO4. NO3 is consumed the fastest by far, and you should dose to get it back or above certain levels.

Here's what I do. When I need an extra water change during the week (for removing detritus, after a big trim to remove leaves, removing algae, mold on driftwood, etc), I make sure to remove the same amount of water I always do weekly no matter what. If I need more water to remove? Tough, it's gotta wait until regular water change day. Then, I dose the "recovery" or "initial" dose, just like I would post-regular-WC.

For example, my recovery dose of Ca is almost always 20ppm, because with a 70% WC at 20ppm, I will have ~26-30ppm Ca in the water:



Doing a midweek WC and dosing the same 20ppm Ca will continue to keep the levels the very same.

It's a bit different for something like NO3, which is consumed a lot more daily, but the gist is the same. Large WC % make this style of maintenance and dosing easy. The larger the WC, the more leniency you get when dosing or recovery dosing.

 

[PeerUnk]

K? Not sure. @Burr740 talks a lot about how K is similar to Ca and Mg, where they need to be present in "X" consistent levels, but aren't actually consumed that much. I've tested that the K in my tanks is usually consumed between 1x and 0.5x the NO3 per week or less, so between 1-2ppm per day? I could be wrong

You could look into the topic of ‘dry weight composition’ of aquatic plants. Growth x composition = uptake.

I did some search myself and noted for potassium (K) it’s roughly equal as Nitrogen (N), so 1/4 of NO3. Beware I found data of species between K = 50-200% of N.

I guess if you use this NO3:K ratio of 4:1, the graph for K is less stable… might be front loaded more and daily dosed less?

 

[Naturescapes_Rocco]

I think I'll start dosing K via this method here:

Journal Post in thread 'Many Lessons || 150x60x60cm, 140gal, Horizontal Reactor High-energy Aquascape Journal'

Oct 29, 2025

Some thoughts on dosing (again, mostly for myself to remember!):​

Currently, I follow the same process with this big tank as I do my smaller experimental tank, where I dry dose my ferts via small cups.
After the 70% WC, I add the DIY GH booster, the initial recovery dose (20-6-26), and midweek after WC I add the booster dose (10-3-13).

However, it gets tedious measuring 2-3 amounts for each cup, multiplied by how many weeks of cups I want to make.
Instead, similar to my experimental tank, I'd like to consider making concentrated liquid ferts that I dose the exact...

• Naturescapes_Rocco

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[ScaperHaynes]

That strategy makes sense too!

Related question… what do you do if you’re going out of town and can’t physically do your weekly water change on the usual schedule?

 

[Naturescapes_Rocco]

If it's for <2 weeks?

Turn the lights down to 10-30%, do an extra large dose of macros (NPK) slightly reduce micros to prevent buildup (20-30% less per daily dose) and hope for the best!

If it's for longer than 2 weeks, I’m not sure! I've always trained someone on how to do water changes at that point.