Landen AquaSoil and KH

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BryceM

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Some of you might be following my 150g build which will be a planted discus setup. I've finally got my Apex Neptune configured, the CO2 reactor and regulator set up, and I've been watching the pH over time. After a 50% WC (3 parts RO to 1 part tap), pH jumps to about 6.70 and then slowly slides downward over time. After 48 hours it's down to about 6.3. From what I'm finding online, Landen is known to eat KH, which isn't a huge deal, but it will take a little fiddling around to keep CO2 concentrations at a reasonable level. I'll be running a low-medium light setup, so I'll have a little leeway, but I'm wondering if this KH drop settles down some over time. There are no plants or livestock in the tank yet.... still getting everything configured.

Anyone track this KH response closely enough to know how it behaves over time?

Here's one 24 hour period after a waterchange. No CO2 during this time:

tNV0jQI.png


Here's another 24 hour period that included a CO2 test for a few hours. The controller maintained the setpoint perfectly, with the expected pH rebound with the CO2 off. During this time, an airstone was running. As you can see, the pH never recovered to the initial level, and started dropping again, as always, as time goes on:

9sRTo7G.png
 
Landen’s buffering definitely mellows out a little from how it is at first. After like 2-3 months I feel it reaches an equilibrium for those like myself with full RO. For those with higher KHs it probably depends how high the KH of the incoming water is. If it’s high enough it will eventually lose most or all of its buffering capacity, same with other aquasoils.
 
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This can get really tricky.

Some depends on the tap water component. What pH does it come out at? Some water companies add CO2 which lowers pH and some add things like Sodium Hydroxide which raises pH. With either the water will come to equilibrium over a day or two.

Then you have naturally occurring pH/CO2 shifts. If I don't add any CO2 to my tank the pH drops at night then rises during the lighting period. Plants are either absorbing or producing CO2. That could help explain the second graphic.

And then you throw in the buffering capacity of the Landen and you see there is lots to consider.

When using a controller to inject CO2 you want these shifts to be as small as possible. That is what led me to go to zero dKH with my Landen, as I didn't want to fight it.

You might want to measure the dKH of the RO/tap mix you are using. If it's very low, then it would not be much to worry about. If it's relatively high then you will have dKH swings which will make a controller pretty much unusable.
 
Sooooo.

Totally agree that it's much more complex than we make it out to be. There are plenty of organic acids, tannins, and such that all affect this in an actual aquarium. It's never a static situation. Even on a good day, pH is a somewhat poor surrogate for CO2 concentration, which is ultimately what we're after.

No water company. Private well. Water usually comes out of the tap at GH 16 KH 12. In my other tank I tried reconstituted RO and had difficulty with the Ca/Mg ratio. Believe me, that caused enormous issues. Mixing RO to tap at 3:1 seems to be working MUCH better.... so that was my plan with this tank. Doing that leaves me at about GH4 KH3.

I'm guessing the Landen stuff will settle down over time. As a low-medium light tank with primarily crypts, anubias, and slow growers, hitting max CO2 at all times probably isn't so important. Probably with discus, it isn't even advisable to push it. At the end of the day, for me, this tank will be primarily about the fish. I've got my 180g to play around with stemmies and such.

There's no reason I can't go with a 4:1 or even 5:1 ratio on this tank. GH of 3 should be plenty and that would bring my KH down even lower, which as you say, will result in smaller shifts. Right now there's nothing in the tank but Landen and a bit of hardscape, so I'm just playing around, getting a feel for the controller and the overall setup.

Plants will be coming in a couple weeks. Fish after that. Discus a couple months later, when I'm sure it's dialed-in.
 
Agree with everything you said. You might consider just using the CO2 flow rate to control pH drop. A controller will be tricky at least until the Landen stops buffering.......which can be a LONG time by the way.

If you go that route, then definitely invest in flow meter if you haven't already. Like you said it you are keeping the pH drop relatively low, that will be better than a controller, especially in relation the health/comfort of the Discus.
 
You may not have posted all your measurements, and all that you know, but from reading your post I have not yet come to conclusion this must be your soil buffering KH. It could be, sure, but if there is another explanation it could be good news and you may still be able to use pH controller after all.

but I'm wondering if this KH drop settles down some over time
Have you actually measured KH drop (I only see pH measurements)?

until the Landen stops buffering.......which can be a LONG time by the way.
I am not a chemist, but if I had this problem I would dump a lot of baking soda, exceedingly high KH, in my tank and let my soil buffer as much as it likes for a week or so. I would hope that after some time whatever does the buffering is tired of it and will not longer actively change my future water. By that time I can refill my tank with water for my plants and fish. Is this a crazy idea?
 
I’ll check the KH before I get too far, but basically, it has to be the substrate. It’s a glass box, PVC pipes, Landen substrate, a few lava rocks, and some manzanita wood. Chemically, it seems improbable for anything but the substrate to be doing this. Also, many others using this substrate have documented the same thing.
 
I’ll check the KH before I get too far, but basically, it has to be the substrate. It’s a glass box, PVC pipes, Landen substrate, a few lava rocks, and some manzanita wood. Chemically, it seems improbable for anything but the substrate to be doing this. Also, many others using this substrate have documented the same thing.
I've been looking at your pH profile, and some of what I see could have alternative explanations. Before giving up on pH controller, it would simplify the equation to have a direct KH measurement. As you probably know, it is easy to get improved accuracy for KH measurements by multiplying the prescribed tank water amount in the test tube, and later divide the number of reagent drops by the same factor. A KH profile during the day (perhaps 4 or 5 measurements) would be helpful to make sure the problem is well diagnosed.

When we do big weekly water changes (I do 70% weekly) it could very well be that KH and pH variations (hardscape, acids in the tank, active substrates etc) can be kept within acceptable range for a pH controller to be used. We sometimes make the mistake in the hobby to agree on qualitative arguments (like 'KH must be stable') rather than quantifying how much variation would still be acceptable for using a pH controller. That's why I believe it is useful to measure/quantify your KH variation, and see what that would mean for a pH/CO2 controller.

BTW, I am not disagreeing that your substrate may be incompatible (at least now) with using a pH controller, but just too stubborn to conclude yet as it would imo be a pity if you can't leverage the great technology you have on your tank :)
 
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I never said I was giving up on the pH controller. Not at all. What I'm seeing here doesn't worry me. It happens with other substrates too. It's just.... interesting. The effect was more pronounced than I expected. No biggie.

I suspect all sorts of pH swings happen all the time in most aquariums. Without a controller that can log it over time, most people probably aren't even aware of it. Through trial and error, "degassed" readings, drop checkers, and watching the fish and plants, most people figure it out eventually. I have Lamotte testing kits, and I'll verify the KH after it sits and percolates another week or two. That's about when the majority of the plants will go in. We haven't even started talking about the calibration of the pH probe, which over time can also wander all over the place.

Another interesting tidbit is how the pH changes during the time I run an air stone overnight. I'm not injecting CO2 at all right now and it still makes a difference, as you can see in the first graph. After the water change and sharp uptick in pH there is a gradual downward trend (substrate sucking up buffering capacity, I think). The downward trend stops suddenly when the air stone kicks on.

Now, I'm aware that there is some organic material in the tank and there is obviously quite a bit of biological activity going on even in the absence of plants and fish. The wood is growing a bit of slime stuff (as it always does, at first) and there is a decent amount of organic material in the Landen substrate. All of that can have an effect too, of course.

If you think about it, one of the primary reasons to do a regular water change is to "iron out" these little things that get imbalanced over time.
 
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