High concentration of ferts decreases the solubility of CO2 in the water - The Planted Tank Forum
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post #1 of 34 (permalink) Old 10-30-2011, 08:24 PM Thread Starter
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High concentration of ferts decreases the solubility of CO2 in the water

I have been thinking on that problem for a while and experimenting with it. And I have made the above conclusion. I haven't seen anything about it on the forum though. What I saw was people complaining about stunted growth whenever they add too much fertilizers. Well I think the reason is the negative dependence of solubility of CO2 in the water with the amount of the ions (salts) already dissolved in the water column. The more salts you have in there already the less the solubility rate of CO2 in the water. And the point when it almost doesn't dissolve anymore is not that far away.
Here is how I came to the conclusion:
Since I started using dry ferts sometimes my drop checker would stay blue no matter the amount of bubbles per second. And pearling would stop, which I particularly fond off. Off course I checked the alkalinity of the water to dismiss possible buffering effect due to presence of alkaline ions. In fact my water is very soft with KH no more than 40ppm and GH no more than 75ppm, and lots of soft water loving plants thriving. Also not only my drop checker stays blue, I see that CO2 in my reactor PHYSICALLY does not dissolve even when I stop pumping CO2 into it, as the amount of bubbles (gas in the reactor) would not decrease. I can literally pump some gas into the reactor in the morning, turn off the needle valve, and after I check the reactor in the afternoon I would see almost the same amount of gas in it. I got a glass reactor, off course, and can see what's happening inside. Oh the reactor is very powerful, it pumps the whole 45-50g of water in my tank 6 times per hour through itself. So it looks like the water just does not take CO2. I also dismissed the temperature as a factor of low solubility as it stays very stable at 74F in my setup.
And it always happens whenever I push the dosage of everything and have around 80ppm-100ppm of nitrates (don't have the test kits for iron and phosphates). I have a huge plant mass and 4.5+ wpg in my tank, so I dose a LOT of ferts and believed going a bit over the limit did not have any drawbacks to it. Well I am just realizing it did. As, I think, the solubility of CO2 in the water is pretty sensitive to the concentration of ferts in there.
Just wanted to share that experience with everyone.

Last edited by yohohon; 11-01-2011 at 04:53 AM.
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post #2 of 34 (permalink) Old 10-30-2011, 09:09 PM
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Interesting theory. Here in my case, I get no more than 20+ ppm of nitrate. I am using more CO2 than usual to get my drop checker to turn lime green. I say my bubble count is closer to 10bps (measured by the bubbles coming out from the CO2 tubing). If from your tinny glass bubble counter, maybe 20+. There are no leaks. I have a huge plant mass. I have 60% of the plants growing very close to the surface. 90% of my substrate surface has plants. I have a 40g. I believe in your case, it is your plant mass driving your CO2 increase. You should increase your CO2 until your drop checker turns lime green. I think your nitrate is high. I bet that if you manage to pump more CO2 until the drop checker to turn lime green, watch the fish too, your nitrate level will drop. My nitrate level is around 20+ ppm. The tank consumes about 5 to 7 ppm per day. I have a 40g tank but I am using dosage for a 40g to 60g tank.

Yes, there is a point in which your reactor and the way in which your CO2 is being dissolved isn't efficient enough due to the amount of CO2 you are injecting. I am using the Ista Max CO2 reactor connected externally. After the CO2 is off, it takes about 30 minutes for all the remaining CO2 to be completely dissolved inside the cylinder. I need to achieve certain high water flow rate to ensure that my entire cylinder does not get too much CO2 inside. This leads to a fair amount of tinny CO2 bubbles to get into the tank.
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post #3 of 34 (permalink) Old 10-30-2011, 09:20 PM
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Interesting theory.

My CO2 diffusion is much less efficient than yours -- just a Do!Aqua glass diffuser underneath a 240gph Koralia Nano powerhead. With my Milwaukee SMS122 pH controller, my pH is maintained at 6.1 for the entire photoperiod. If I put some tank water in a container and let sit for 48 hours, my "actual" pH is 7.7-7.8.

Now, my tank is a very high light experiment, running 4x54W of the strongest T5HO lighting (ATI Powermodule - made for reef tanks), the lights at 12" from the water surface. With this much light, I have to pump soooo much CO2 and sooooo much dosing every other day. Check it out:

1 tbsp GH booster [12ppm potassium, 5 ppm calcium, 0.89 ppm magnesium]
1 tsp of KN03 [15ppm of nitrates, 9.6ppm potassium]
1 tsp of KH2P04 [19ppm of phosphates, 7.82 ppm potassium]
(potassium totals to 29.42ppm)

CO2 is at approximately 47.7ppm. I know the KH/pH/CO2 calculator is not 100% accurate, but it's a pretty good estimate, considering my 1.6 drop in pH.

No problems with solubility here --
CO2 - 47.7ppm
K - 29.42ppm
N - 15ppm
P - 19ppm

Perhaps your dosing levels are even higher than mine?

Tank is 120cm x 45cm x 45cm. 4 yr old Aqua Soil, a few pieces of driftwood, and tap water treated with Prime. pH is 7.7-7.8, but goes down to 6.1 during photoperiod. KH 2, GH 6.


Oh, with the API Nitrate test kit, the water crimson red for me.....so over 80ppm? I really need to make reference solutions to get a more accurate reading of my nitrates, before my dosing. I do know that less than what I'm dosing right now leads to diatoms, which goes away after I bring my nitrate dosing back up.
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post #4 of 34 (permalink) Old 10-30-2011, 10:01 PM
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Originally Posted by zergling View Post
Interesting theory.

My CO2 diffusion is much less efficient than yours -- just a Do!Aqua glass diffuser underneath a 240gph Koralia Nano powerhead. With my Milwaukee SMS122 pH controller, my pH is maintained at 6.1 for the entire photoperiod. If I put some tank water in a container and let sit for 48 hours, my "actual" pH is 7.7-7.8.

Now, my tank is a very high light experiment, running 4x54W of the strongest T5HO lighting (ATI Powermodule - made for reef tanks), the lights at 12" from the water surface. With this much light, I have to pump soooo much CO2 and sooooo much dosing every other day. Check it out:

1 tbsp GH booster [12ppm potassium, 5 ppm calcium, 0.89 ppm magnesium]
1 tsp of KN03 [15ppm of nitrates, 9.6ppm potassium]
1 tsp of KH2P04 [19ppm of phosphates, 7.82 ppm potassium]
(potassium totals to 29.42ppm)

CO2 is at approximately 47.7ppm. I know the KH/pH/CO2 calculator is not 100% accurate, but it's a pretty good estimate, considering my 1.6 drop in pH.

No problems with solubility here --
CO2 - 47.7ppm
K - 29.42ppm
N - 15ppm
P - 19ppm

Perhaps your dosing levels are even higher than mine?

Tank is 120cm x 45cm x 45cm. 4 yr old Aqua Soil, a few pieces of driftwood, and tap water treated with Prime. pH is 7.7-7.8, but goes down to 6.1 during photoperiod. KH 2, GH 6.


Oh, with the API Nitrate test kit, the water crimson red for me.....so over 80ppm? I really need to make reference solutions to get a more accurate reading of my nitrates, before my dosing. I do know that less than what I'm dosing right now leads to diatoms, which goes away after I bring my nitrate dosing back up.

All I can say is that use a drop checker. Until then, you really don't know how much CO2 you have in your tank. I used the API kit too. I can verify that the accuracy is pretty close judging from how much I dose and what ppm nitrate concentration I should be getting.
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post #5 of 34 (permalink) Old 10-30-2011, 10:26 PM
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Yohohon, that is interesting.

Any chance you could do some more tests? Assuming your nutrient level is still high, do a 75% water change to cut the accumulated nutrient levels. Dose nothing that day. On the next day, dose nothing again, and check the CO2 dissolution rate. If you're correct, it should be excellent on that day. I'd arrange several tests of that nature, perhaps even keeping a daily log to see if there's a clear correlation.

I've been reading lots of threads on stunting since my experience with Ammania gracilis. In brief, I spent three months trying to make it grow properly; during which time I tried the EI approach of "add more" on almost every conceivable combination of nutrients, with no success. And all the while the person I got it from, who is local to me and shares the same water supply and a very similar tank setup, but doses much lighter than EI, was growing it like crazy.

What I've found in those threads is that most people are confused just like I am. But a few claim to have found that required nutrient levels are dependent on hardness. With hard water, more nutrients are required to avoid deficiencies; and with soft water, less nutrients are required to avoid stunting. Whether that's true, I don't really know; but I figured I'd mention it since it's potentially applicable to your situation.
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post #6 of 34 (permalink) Old 10-30-2011, 10:36 PM
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Yohohon, that is interesting.

Any chance you could do some more tests? Assuming your nutrient level is still high, do a 75% water change to cut the accumulated nutrient levels. Dose nothing that day. On the next day, dose nothing again, and check the CO2 dissolution rate. If you're correct, it should be excellent on that day. I'd arrange several tests of that nature, perhaps even keeping a daily log to see if there's a clear correlation.

I've been reading lots of threads on stunting since my experience with Ammania gracilis. In brief, I spent three months trying to make it grow properly; during which time I tried the EI approach of "add more" on almost every conceivable combination of nutrients, with no success. And all the while the person I got it from, who is local to me and shares the same water supply and a very similar tank setup, but doses much lighter than EI, was growing it like crazy.

What I've found in those threads is that most people are confused just like I am. But a few claim to have found that required nutrient levels are dependent on hardness. With hard water, more nutrients are required to avoid deficiencies; and with soft water, less nutrients are required to avoid stunting. Whether that's true, I don't really know; but I figured I'd mention it since it's potentially applicable to your situation.

So, are we saying that the nutrient balance is out of the proportion given with certain water hardness level...resulting in certain issues with the plant's nutrient uptake ability? Well, my Staurogyne repens are experiencing stunt growth since it has been planted 3 weeks ago. Each stem has good and long roots but they didn't "explode" with growths.
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post #7 of 34 (permalink) Old 10-30-2011, 10:59 PM Thread Starter
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DarkKobra, my experience with water changes does confirm the claim. As when I do a substantial water change and don't dose anything right away, the CO2 starts dissolving faster (I see it not building up in the chamber) and the drop checker reacts appropriately. The water change I did today was that last piece of evidence that made me go public with the claim here.
I used to do a lot of chemistry in school, including hydrolysis, and it makes lots of sense to me. Ultimately there is a point of saturation for the water, when it would not dissolve anymore salts(i.e. take anymore ions), and CO2 in terms of dissolution in water behaves like any salt, only it is slower to dissolve. The question is where is this point for CO2. And my claim is it is not that high up, pretty achievable for a planted tank.

Last edited by yohohon; 11-01-2011 at 04:53 AM.
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post #8 of 34 (permalink) Old 10-30-2011, 11:22 PM
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Originally Posted by yohohon View Post
DarkKobra, my experience with water changes does confirm the claim. As when I do a substantial water change and don't dose anything right away, the CO2 starts dissolving faster (I see it not building up in the chamber) and the drop checker reacts appropriately. The water change I did today was that last piece of evidence that made me go public with the claim here.
I used to do a lot of chemistry in school, including hydrolysis, and it makes lots of sense to me. Ultimately there is a point of saturation for the water, when it would not dissolve anymore salts(i.e. take anymore ions), and CO2 in terms of dissolution in water behaves just like any salt, only it is slower to dissolve. The question is where is this point for CO2. And my claim is it is not that high up, pretty achievable for a planted tank.

But did you ever manage to get your drop checker to turn lime green with EI dosing? Sure, we pump more CO2 if having too much fert can cause CO2 not to dissolve quickly. CO2 is cheap. I would certainly not decrease my EI dosage just because I may need to use more CO2. EI dosing is about excess.
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post #9 of 34 (permalink) Old 10-30-2011, 11:31 PM
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Originally Posted by yohohon View Post
DarkKobra, my experience with water changes does confirm the claim. As when I do a substantial water change and don't dose anything right away, the CO2 starts dissolving faster (I see it not building up in the chamber) and the drop checker reacts appropriately. The water change I did today was that last piece of evidence that made me go public with the claim here.
I
However, did you rule out the fact that your source water may not be saturated with O2 to begin with? Did you age the water with an air pump? Or just treated the tap water and immediately do a water change? I am from NYC and our water has undetectable nitrate. For you to accumulate up to 100 ppm of nitrate, it is either your plants aren't using it or your test result isn't accurate. Or you are dosing too much nitrate more than your plants can consume. Much more...
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post #10 of 34 (permalink) Old 10-30-2011, 11:47 PM Thread Starter
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But did you ever manage to get your drop checker to turn lime green with EI dosing? Sure, we pump more CO2 if having too much fert can cause CO2 not to dissolve quickly. CO2 is cheap. I would certainly not decrease my EI dosage just because I may need to use more CO2. EI dosing is about excess.
Oh yeah, sure. Before I started using dry ferts and during the time, when I was cautious with them at the beginning and was following recommended dosage schedules, I had consistently had lime green situation. During those times sometimes I would even have the situations of too much CO2 and have my fish gasping for air. Not anymore. No matter how many bubbles per sec I ramp up, co2 just builds up in the chamber, doesnt want to dissolve. Also, as I said, during the recent period of high dosage I can only get the drop checker green (not lime green, just green) when I do a WC.

Here is the picture taken after a 50-60% WC. Hence the abundant pearling. You can see the drop checker is green (rare thing lately, as I said). My reactor is in the back.
Also visible is one tonina on the right is getting yellow, which I believe due to the CO2 deficiency during the last 3-4 weeks of having the described problem. All other toninas are not doing very well lately too. Before I stepped up dosage, however, they were growing like crazy and this whole forest came about in just one month from just 1 plant of each of the kind of toninas on pic. My HC, another CO2 sensitive guy, is also stunting during that period.


Last edited by yohohon; 10-31-2011 at 01:49 AM.
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post #11 of 34 (permalink) Old 10-30-2011, 11:56 PM
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Oh yeah, sure. Before I started using dry ferts and during the time, when I was cautious with them at the beginning and was following recommended dosage schedules, I had consistently had lime green situation. During those times sometimes I would even have the situations of too much CO2 and have my fish gasping for air. Not anymore. No matter how many bubbles per sec I ramp up, co2 just builds up in the chamber, doesnt want to dissolve. Also, as I said, during the recent period of high dosage I can only get the drop checker green (not lime green, just green) when I do a WC.

Here is the picture taken right after a 50-60% WC. Hence the abundant pearling. You can see the drop checker is green (rare thing lately, as I said). My reactor is in the back.
Also visible is one tonina on the right is getting yellow, which I believe due to the CO2 deficiency during the last 3-4 weeks of having the described problem. All other toninas are not doing very well lately too. Before I stepped up dosage, however, they were growing like crazy and this whole forest came about in just one month from just 1 plant of each of the kind of toninas on pic.

Nice tank....what reactor you use? What is your nitrate level the day before your weekly water change?
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post #12 of 34 (permalink) Old 10-31-2011, 12:11 AM Thread Starter
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Nice tank....what reactor you use? What is your nitrate level the day before your weekly water change?
Thanks! That's just 1/3 of it))
I don't know what is the brand of the reactor, but the pump is rated at 300 something GPH. Nitrates, as I said, are around 60+ppm up to 100, which depends on how compulsive I was at dosing during the week)). The test solution turns very very red, when I started pushing things. I did not calibrate it per se, but it's been consistent with what I see happening in the tank, and I have been using it for 5 months now, so I learnt how to read it.
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post #13 of 34 (permalink) Old 10-31-2011, 12:36 AM
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DarkKobra, my experience with water changes does confirm the claim. As when I do a substantial water change and don't dose anything right away, the CO2 starts dissolving faster (I see it not building up in the chamber) and the drop checker reacts appropriately. The water change I did today was that last piece of evidence that made me go public with the claim here.
But does this also extend to the day after the water change? Given the unknown concentration of dissolved gasses in tapwater, I would ignore the results for the same day as the water change itself, giving the tank a day to settle into normal concentrations. Water changes can also induce "false pearling" for most of a day.

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Originally Posted by yohohon View Post
I used to do a lot of chemistry in school, including hydrolysis, and it makes lots of sense to me. Ultimately there is a point of saturation for the water, when it would not dissolve anymore salts(i.e. take anymore ions), and CO2 in terms of dissolution in water behaves just like any salt, only it is slower to dissolve. The question is where is this point for CO2. And my claim is it is not that high up, pretty achievable for a planted tank.
I've forgotten more of my school chemistry than I still remember. But I think CO2 doesn't behave exactly like dissolved solids or salts. I know for certain it doesn't register on a TDS test, and neither CO2 nor O2 will displace each other.

There is a complex equilibrium between CO2, carbonic acid, and carbonates; with carbon shifting between the forms based on pH. However, most of the "dissolved" CO2 in a tank continues to exists as single molecules of CO2; and does not split into ions, like salts do in a polar solvent (water).

Not to say that it's impossible that high TDS might somehow affect rate of CO2 dissolution. Frankly, I don't know. I just think the salt analogy isn't enough to make an assumption as to the mechanism.
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post #14 of 34 (permalink) Old 10-31-2011, 12:48 AM
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So, are we saying that the nutrient balance is out of the proportion given with certain water hardness level...resulting in certain issues with the plant's nutrient uptake ability?
From what others are saying, who have actually had stunting problems and solved them by deviating substantially from typical EI dosages, this seems to be the case.

I'm not certain if it's really true. To do that, I'd have to run a totally different set of experiments than the three months I mostly spent increasing dosages other than phosphates; and all my Ammania is dead.
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post #15 of 34 (permalink) Old 10-31-2011, 01:10 AM
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Looks like a Plantguild reactor

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