CO2 and Ph

dR3ws3r

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Hi,

I have a 2 month old setup that I've been using for aquascaping. It is a 25 gallon tank with driftwood and aquasoil. I run CO2 during the light period at about 1 bubble a second (estimate). My drop checker is a good shade of green. I recently started testing my water, and noticed it is very acidic. The odd thing is that my tap water is between 7.2 - 7.4 (using a calibrated apex probe). So after testing for KH and DH I found that they are basically 0. Adding one drop in the test kit changes the color. If I understand things, I am guessing that the lack of minerals in my water is providing me with no buffer. So when adding things like CO2 I am getting rapids swings in my PH, and my new fish are not doing well. This morning I adding a filter (hanging box filter) with only crushed coral in it to see if I can add some buffer to the tank. After running it for a few hours, the KH has gone up to 4 and the PH has come up from 5.6 to 6.2.

I don't want to keep swinging things so wildly and would be happy to get my water in the tank anywhere near 6.5. I feel bad for the fish because they appear to be hiding. Am I on the right track? Or am i just chasing PH?

It seems that anything I do, whether injecting CO2 or adding crushed coral is causing big swings. Will the increase in KH eventually allow me to inject CO2 without causing big fluctuations in PH? It just seems crazy that my tap is 7.2-7.4 but the tank was at 5.6.

Any advice or comments are appreciated.

Thanks,

Drew
 

Byron

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You give the explanation correctly. GH and KH influence pH, and when the GH/KH are zero the pH is free to do what it likes, and this is when it is subject to other factors, like CO2. CO2 produces carbonic acid so the pH lowers.

The issue is far more than mere buffers. And crushed coral is not an adequate buffer, you need something like dolomite which has magnesium as well as calcium; the latter alone as with crushed coral and similar can reach the capacity and then crash. Also, if fish are present (as opposed to just plants) they should be the focus. What fish species do you have in this tank? Very soft water and most soft water species will thrive in zero GH. Harder water species will not.

There is a natural pH fluctuation diurnally, in nature and even more (usually) in planted tanks. This is obviously not a problem provided it is not extreme, which it can be with diffused CO2.
 
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dR3ws3r

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Thanks for replying. I started with some fish I thought would be pretty simple. Ottos, which are all doing fine it appears, cory's all 3 of which died, and neons (a few of which have died).

I would be fine with keeping it soft and acidic, but 5.5 in the peak of the night seemed pretty low, and the neons don't really seem to be thriving. I wanted to add crushed coral to raise the ph to middle sixes and to add some stability.

I wouldn't expect the driftwood to be the culprit as it has been in there for 2 months and from what I've read the release of tannic acids usually slows over time. I do notice that when I start CO2 injection, even at a low rate, the PH starts dropping. I was hoping that there was a fairly easy way to keep the PH from dropping more than say .1 or .2 every time I add CO2. Thus the attempt to raise the KH and buffer against the Carbonic Acid effect. At this point though, I am open to any ideas. It is like every time a try to plug a leak another one appears (metaphorically).
 

Byron

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First, the fish will thrive in zero GH/KH and an acidic pH. All three come from such water.

Neon problem may be just the terrible genetic state of this inbred fish. Depends what else may be the problem. They would likely react negatively to any fluctuation in pH caused by CO2.

Tannins is not the issue with wood. All organic matter, be it wood, dried leaves, peat, dead plant and animal matter, etc, produces CO2 as it decomposes which is a continual process. This is never a problem in tanks with very soft water and fish suited to such water. Back in the 1990's I was "convinced" by (I'm sure) well-meaning aquarists to buffer two of my tanks, and I used about three or four tablespoons of dolomite in a nylon bag in the canister filer, which kept the pH around 6.4 to 6.5 whereas without this it was 5 or lower. After several years, I moved and gave this up as a pointless waste of time. The fish I keep have evolved over thousands of years to function best in water with a GH and KH of 0 and a pH of 4-5; if I can provide similar, the fish will be healthy.

I am not a fan of CO2, there are more and more sources now warning of the negative effects on fish. I have seen my cories increasing respiration solely because of the increase of natural CO2 during the night in fairly well-planted tanks (that have no artificial CO2 added at all).
 
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dR3ws3r

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well last night I turned off the filter with the crushed coral in it. I did no CO2 injection during the day, and the ph dropped from 6.4 down to 5.98 and is still fallling.

I know that plants give off CO2 during the evening, but that seems like a big drop.

Could there be something else in the tank making the water so acidic? Other than the big hunk of driftwood I have aqua soil and some lava rock, but I would not expect that they would mess with my ph so much.

I have no idea what to do at this point.
 
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dR3ws3r

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Additionally I checked and my kh actually went from 4 to 2 overnight. Could there be so much acid in the tank that the dissolved calcium solids were eaten away overnight. This once again (without a wealth of experience on my ) seems pretty extreme.
 
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dR3ws3r

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Who do you water change your tank.
I'm not sure what you mean by "who"? I do the water changes. I started doing about 50% every other day for the first month of the tank (because of the aqua soil), and am currently doing 20% every 2nd to 3rd day. I was "hoping" the tank would settle out and I could do 25% once a week.
 

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I think some general info on this might help with the understanding of what is occurring here.

First, the source (tap) water will have a GH, KH and pH value. These are determined by the water source. "Pure" water falls as rain and snow, but water is a powerful solvent so it easily assimilates substances as it falls (like CO2) and on the ground. If the water flows over or through calcareous rock (like limestone) it will dissolve and assimilate calcium and magnesium, increasing the GH, KH and pH. If it falls on non-mineralized earth it will assimilate organics and be soft or very soft with an acidic pH.

When initially put into an aquarium, the GH, KH and pH values will be those of the source (tap) water. The natural biological processes in an aquarium with fish that are fed creates organic matter, and raises the CO2 which produces carbonic acid so the pH will tend to lower. However, the extent to which this acidification occurs depends upon the GH and KH, along with other factors. But the GH/KH are primary; the higher these are, the more they serve to "buffer" the pH, preventing it from lowering. Organic matter like wood, dried leaves, and fish waste produce CO2 as they decompose. A calcareous substance such as a substrate composed of calcareous mineral or chunks of calcareous rock will work to add dissolved minerals to the water and raise the GH/KH/pH. In both cases the initial GH/KH/pH are the starting point and will determine the extent to which the processes play out.

Stability in parameters is the key to a successful aquarium. Nature (chemistry, biology) will govern this, in accordance with the factors mentioned above, provided we do not interfere. As soon as we do, by attempts to increase or decrease the GH/KH/pH, we are offsetting the processes, which is always risky because of other factors, but also the stability of the system is being "adjusted" in some way.

You said previously that the GH and KH are basically zero, and I assume this is the tap water, so the pH will naturally be free to lower as the biological processes increase the natural CO2.
 

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Additionally I checked and my kh actually went from 4 to 2 overnight. Could there be so much acid in the tank that the dissolved calcium solids were eaten away overnight. This once again (without a wealth of experience on my ) seems pretty extreme.

If your KH fell from 4 to 2 then CO2 is probably not the source of most of the acidity in your tank.. CO2 will not cause a KH drop. tyipically carbonate is typically and magneisum carbonate in the water. Calcium carbonate does register on a GH test since it has calcium. It also registers on the KH test because of the carbonate. But if you have excess sulfate in your water the then excess sulfate in the water will react with calcium carbonate forming calcium sulfate . Calcium sulfate will register on A GH test but not on a KH test. Tannic acid and excess chlorides your wate can also cause a KH drop.\.

ironically your plants maybe causing the PH drop. Plants need a lot of potassium to grow. if your water or fertilizer has potassium sulfate the plants will consume the
potassium and only a little bit of culture. So much of the sulfur wil stay in the water and that that can cause the pH drop you are seeing. IN my aquarium I am using DI water so I need to add calcium and magnesium sulfate to create a sable GH for fish. but it also used my PH to drop. In a way your PH drop is a good thing because it is a good indication of growing plants.

I also had to deal with this issue in my tank. My solution was to put a sea shell in my filter to that It was nurtrallize the Excess This keeps my PH consistently near 7. So you were on the right track with the coral. But instead of leaving it in for a few hours I leave it in there all the time and only replace it about once a year or when it fully dissolves away.. The shell will only dissolve when there is excess acid in the tank. It won't do anything once the PHraches 7.

Not as to your CO2 system it is very wistful methode of adding CO2 to water and if you get too much in the water you will kill your fish. I use the inverted bottle methode for adding CO2. You cannot kill your fish fish with this methode and I only use about 1/4 of the CO2 I used to use. I basically placed a bottle inverted in the the tank with no air in it. and then filled it with CO2. Your water will pull the CO2 out gradually. SOMe people use large bottles and manually refill them once a day. IN my small agaurium I initially used a small battle but found it needed refilling about once 4 times a day.. So it is now on a timer and is refilled automatically. If the bottle is overfilled the excess bubbles out to the surface and safely disipates into the air. You also no longer need a drop checker in the tank
 
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dR3ws3r

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Thanks for the reply, I need to digest that a little.

As an update, I watched the tank parameters for 2 days without any CO2 injection. During the photo period (8 hours) the PH would rise about .3-.4 on the scale. In the non-light period the PH would drop .4-.5 over the 16 hour period. It appeared to this layman that the CO2 being absorbed by the plants during the light period was being undone by the respiring in the evening, and that the Carbonic Acid was responsible for the PH changes. So last night I put an airstone on a timer and let it run all night. The PH hardly moved during the dark period, from 5.92 - 5.89. A huge improvement in stability at least for one night. I will keep it on a timer and see what happens over the next day or two.

I have noticed a little film on the top of the water, and was wondering if it was algae, or something else. I have a fluval canister filter and I have a lily pipe outlet that is just below the water line, because of the noise when it is on the water line. There is plenty of water movement, but maybe the CO2 just wasn't escaping due to the film and the location of the filter outlet? Guessing here.

Another thing I find a little odd is that my tap water has a ph of 7.2-7.4 out of the tap, but if I merely set it in a glass and let it sit for 24-48 hours it will go down to 6.3-6.4. From what I have read in forums and such, that is the opposite of what most people see. I'm not adding dechlorinator in the glass, and i'm not sure of the effect of the changes in ph to the water (in the glass) as the chlorine leaves the solution.

And on another note of curiosity/annoyance I measured the tap water this morning. PH 7.3, DH 4. GH 4. I am using the API drop test. I know that the water two days ago took 1 drop to change color on the DH test. Do other water utilities have such volatility in their water? We have pex plumbing in the house which is basically pvc pipes with brass elbows. I wouldn't think that would affect the water quality ... but I have no idea anymore.

Thanks for all the help and for listening to my chemistry rants. This is pretty frustrating and confusing.
 

Colin_T

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A big piece of driftwood might contribute to the pH dropping, as might soil, some of which can contain peat or other things that break down.

The coral rubble in the filter should help but you might need more of it or add some KH buffer to get the KH up and this should help stabilise the pH.

A lot of people that have planted tanks and use CO2, will have the KH around 100-150ppm so the pH doesn't fluctuate.
 

Byron

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Another thing I find a little odd is that my tap water has a ph of 7.2-7.4 out of the tap, but if I merely set it in a glass and let it sit for 24-48 hours it will go down to 6.3-6.4. From what I have read in forums and such, that is the opposite of what most people see. I'm not adding dechlorinator in the glass, and i'm not sure of the effect of the changes in ph to the water (in the glass) as the chlorine leaves the solution.

This could be due to the water authority adding something to increase the pH (but not affect GH/KH). I have this issue, and it is not uncommon in areas where the source water is very soft and thus likely acidic. The higher pH is intended to reduce/eliminate corrosion problems. The pH will tend to settle out in a day or two, depending.

I have noticed a little film on the top of the water, and was wondering if it was algae, or something else. I have a fluval canister filter and I have a lily pipe outlet that is just below the water line, because of the noise when it is on the water line. There is plenty of water movement, but maybe the CO2 just wasn't escaping due to the film and the location of the filter outlet? Guessing here.

This is a protein film. It is common in planted tanks. I have seen it very substantial in some tanks, but never occur in others, all being planted. You want to reduce it as much as you can, because it can impede the gaseous exchange. I found turning the water changer upside down in the tank with the large opening at the surface will pull this in, though it is a slow process.
 

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As an update, I watched the tank parameters for 2 days without any CO2 injection. During the photo period (8 hours) the PH would rise about .3-.4 on the scale. In the non-light period the PH would drop .4-.5 over the 16 hour period. It appeared to this layman that the CO2 being absorbed by the plants during the light period was being undone by the respiring in the evening,
Yeas I have seen the PH move up with lights on. I believe that when the lights are on the plants are possibly consuming carbonate (converting calcium carbonate to calcium hydroxide) This would push PH up. But with the lights on my PH dropped back to to very close to like 6.7 to 7This could be explained by the calcium hydroxide reacting wtihCO2 and converting back to Calcium carbonate.

Your PH drop is little more than in my tank but I have had at least one snail shell in the tank for about 2 years.you tank hasn't been running as long and may have some acid buildup in the substrate. So the night time drop may become less over time. Or it could be due to the driftwood which I don't have. Either way a PH drop-off fo 0.5 is a lot better than a drop of 1 or more. Inever saw anything in the behavior of my shrimp that could be linked to the small PH change I have. Also When I first saw the PH increase it was going up to 8 with the lights on. I dimmed the light to minimize the PH PH increase.

The coral rubble in the filter should help but you might need more of it or add some KH buffer to get the KH up and this should help stabilise the pH.

The corral is solid KH. It won't register on a KH test.but CO2 and other things may cause a small amount to exist as dissolved KH i the tank. But in my tank it is not that much. I would not use commercial KH boosters since they are generally made with potassium bicarbonate. In nature most of the carbonate is from calcium and magneisum carbonate. Excessive levels of Potassium can harm fish. And potassium bicarbonate can increase PH to well avbove 7 while calcium and magnesium carbonate cannot are limited to a maximum PH of about 7.

I have noticed a little film on the top of the water, and was wondering if it was algae, or something else. I have a fluval canister filter and I have a lily pipe outlet that is just below the water line, because of the noise when it is on the water line. There is plenty of water movement, but maybe the CO2 just wasn't escaping due to the film and the location of the filter outlet? Guessing here.
This film is often called a protean biofilm. My understanding is that it is mainly bacteria floating on the surface of the water. Altering your filter outflow to creat ripples on the surface of the water often breaks it up. I don't think it will have any significant influence on CO2 but I haven't looked into that. I just make sure I have enough surface agitation to eliminate it.

Another thing I find a little odd is that my tap water has a ph of 7.2-7.4 out of the tap, but if I merely set it in a glass and let it sit for 24-48 hours it will go down to 6.3-6.4.
Yes water utilities do add things to increase PH to help prevent pipe corrosion. But I have never heard of thePH dropping when it is sitting in a bucket. Most of the time the PH actually starts out a little low then increase after a day for so.
 
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dR3ws3r

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I ran into this article while trying to better understand my tank parameters, and they give what I would "generally" consider a slightly different take on things. https://www.2hraquarist.com/blogs/ph-kh-gh-tds/kh-explained. To paraphrase they say PH swings can happen routinely in nature in soft water conditions, and that the more important parameter to monitor is kh. The also include some research that shows nitrifying bacteria can live in very low PH conditions in an attempt to debunk the idea of PH crashes.

Having now tested my tap water for about 5 days I have seen water that takes 1 drop of API solution to turn color and water that takes 5 drops of API solution to turn color. So somewhere between 0.5 - 4.5 kdh in my mind. If indeed my testing is sound, which I would think I'm being pretty careful, does it make sense to use RO water and remineralize? I don't know much about that subject other than what I have read and am wondering if anyone reading this has had success doing that. I wouldn't say that cost is "really" a factor as I don't think that installing an RO system in one of my sink areas would be prohibitively expensive. I imagine you would use some combination of seachem equilibrium (as an example), and seachem kh additive to dial in a number. Somehow "creating" my own brew seems kind of unnatural and that perhaps there are things missing by doing it this way. Just as a general question, will these buffers provide all the minerals and other unknown quantities that the fish and plants in the aquarium need to be healthy?

I have still shied away from CO2 injection thus far. Monitoring my ph and using an airstone during the non light phase has kept my ph between 5.8 and 6.0 over the 24 hour cycle with the rises still occuring during the photo period and most of the ph drop occurring in a 3hr window after the light turns off. The kh in the aquarium is still at 0-1 which I wouldn't expect to change. I plan on trying to use some crushed coral in a filter this weekend to try and add some alkalinity to the tank slowly.
 

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