CO2 Levels

[Bunny13]

My CO2 levels are at 30ppm which, when I look at the charts, is a little high. However, my fish aren't showing any signs of distress and my plants don't pearl. My pH is 6.6 and my kH is 4. Also, in case it makes a difference, my gH is 10. I currently have I do have 2.4 watts over the tank and I am adding a 1/4cup of coral in my filter to help my snails. Could the coral be affecting it somehow?

[TwoTankAmin]

Yes- the coral will throw off the pH/kh method of trying to measure co2 levels because of its effects on these two numbers.

[rich311k]

Leave a cup of tank water out for 24 hours and measure the change in PH. It will give you some idea where you are. I think 30ppm is a perfect level. I start to worry if gets near 40ppm. From what I have read 90 -100 is the dangerous levels but I would rather not find out.

[joephys]

30ppm isn't that high. It could be much higher and the fish would be fine.

The best method is to measure the pH/kH in the tank, then take a small cup of water, let it sit out over night and measure it in the morning to see how the pH changed. That should give you a better idea of the CO2 level.

[Roan]

Just a note in case someone reads this thread and isn't aware --

Anything over 25ppm is pushing it big time with rainbowfish. They are very oxygen intensive. Best is 20ppm, no higher.

Roan

[RTR]

The crushed coral will affect the pH/KH of the water (the reason it is used), but that will not affect the CO2 reading itself, As the KH of the water must be measured, so that the CO2 computation itself will not be adversely affected - it will be accurate. The concentration of CO2 is not affected by the source of the carbonates/bicarbonates, only by their level in the water at the time of reading.

Aging or aeration a tank water sample will give better data, but is not instant-reading. It does compensate for the non-volitle organics (which do affect the pH) in the water, as their concentration should not shift with aging.or aeration.

[TwoTankAmin]

How can it not effect the reading?? When I set up my co2 added tank my tap water was pH 7.4 and KH5 from the tap. However, in testing other tanks, I had noticed that my KH had a tendencey to drop over time to about 2. This despite doing weekly 40% (on average) water changes. I was concerned about this because I though that adding co2 would be more likely to result in a pH crash.

So I added about 3/4 of a cup of crushed coral to my Eheim about a week or two before hooking up the co2 tank. The effect was to raise the KH 2 dgs but the pH barely moved. Once the co2 was on the tank I began testing the pH to determine the effects of the gas and to determine if I needed to do anything about nightime levels.

The upshot was at the rate I ran the co2, I didn't have much to worry about. The tank thrived and the plants pearled. However, when I tried to test the co2 levels via the pH/KH method, it showed co3 levels to be much lower than would be required to keep the plants I had growing well and pearling the way they did.

The only explanation I could come up with for the disparity between the "purported" low co2 level and the actual plant health and growth was that the pH/KH method was not reliable due to the crushed coral in the filter distorting the readings.

I have long since stopped adding the crushed coral once I understood that the risk of a pH crash was remote at best.

However, my understanding of the nature of KH comes from the following from the FINS site:

Buffering capacity refers to water's ability to keep the pH stable as acids or bases are added. pH and buffering capacity are intertwined with one another; although one might think that adding equal volumes of an acid and neutral water would result in a pH halfway in between, this rarely happens in practice. If the water has sufficient buffering capacity, the buffering capacity can absorb and neutralize the added acid without significantly changing the pH. Conceptually, a buffer acts somewhat like a large sponge. As more acid is added, the ``sponge'' absorbs the acid without changing the pH much. The "sponge's'' capacity is limited however; once the buffering capacity is used up, the pH changes more rapidly as acids are added.

I also though that the pH drop from adding co2 is due to the fact that some of it is converted to carbonic acid and it is this acid that lowers the pH. Since the pH/KH method of measuring co2 levels is based on the absolute values, why would something that has the opposite effect of co2 on pH and KH not distort the levels and thus make the test inaccurate?

[Bunny13]

I let a cup sit out over night and when I tested the pH this morning it was at 7.0. So, putting this in the chart I'm getting a reading of 12ppm co2 which is better but a little on the low side. It makes more sense though, with the way my fish and plants were acting.

[RTR]

TTA - you are working under and handicapped by unjustified assumptions. The pH/KH/CO2 test assumes that no other significant acid is present, and that is obviously not the case for many to most fish tanks.

This test is not a direct measure of CO2, It is a measure of the difference of the observed pH versus the expected pH from the pH expected at a given and immediately tested KH.
- You must have an immediate reading of the KH currently in the tank, not that of the tap water if you have modified the water in the tank (as by aragonite or crushed coral or bicarb or limestone addition). Nor can you guesstimate the KH from the post-partial KH observed at some other time, it is a now reading.

Tanks generate acids. These in practice tend to be fairly stable within some range dependent of the the frequency and percentage of the partials, the stocking, feeding, and all the usual suspects. But it is not a stable figure, it is a range. If you assume that your current acid levels are those observed immediately post partial, you CO2 reading will be off on the high side. If you assume that your acids are at immediately pre-partial readings, you CO2 reading will be off on the low side. If you assume they are always trivial, your readings for CO2 are meaningless, just as Bunny13's tests have shown in this thread.

Always examine the assumptions. Hobbyists generally have a really hard time with that one, and it is an honest mistake. They are told all sorts of things which are valid under certain conditions, but very, very rarely told how to check those assumptions. On CO2 that is how and why so many hobbyists report sedative to potentially lethal CO2 levels which are observably not valid. A level of 30ppm CO2 is neither of those negatives, but it quite different in results from 12 ppm CO2, which turns out to be closer to the fact in this thread.

HTH

[TwoTankAmin]

RTR- I think that was the point I was trying to make. Lets assume one could set up two virtually identical co2 added tanks which had only one difference- one has crushed coral added and the other does not. All other things being equal, I would ecpect they would not give pH and KH test results that were identical.

Based on the chart on thekrib.com, I believe that for any given pH level, the higher the KH the higher the level of co2 will be. The converse is that at any given level of KH, the lower the pH, the greater the level of co2 is.


My point is that the use of crushed coral, especially when it is a smaller amount that changes the KH levels a bit but barely moves the pH, the less reliable the pH/KH test for co2 levels will be.

[rich311k]

This is a great read guys.

Bunny I would up the CO2 try to get it around a steady 20ppm. After a while if you want to push it more you can, but 20 is safe and the plants will like it.

[wesleydnunder]

I'm confused here, TTA. I thought increasing KH, with carbonate or bicarbonate, had a corresponding rise in ph.

Mark

[Roan]

Originally Posted by wesleydnunder

I'm confused here, TTA. I thought increasing KH, with carbonate or bicarbonate, had a corresponding rise in ph.

Mark

It should have, yes, up to 1ppm, however other acids present in the tank could and can affect the pH reading without changing the KH reading.

My 2 cents
Roan

[TwoTankAmin]

Here is the full text from FINS re raising GH and/or KH:

Altering Your Water's Chemistry

Hardening Your Water (Raising GH and/or KH)
The following measurements are approximate; use a test kit to verify you've achieved the intended results. Note that if your water is extremely soft to begin with (1 degree KH or less), you may get a drastic change in pH as the buffer is added.
To raise both GH and KH simultaneously, add calcium carbonate (CaCO3). 1/2 teaspoon per 100 liters of water will increase both the KH and GH by about 1-2 dH. Alternatively, add some sea shells, coral, limestone, marble chips, etc. to your filter.

To raise the KH without raising the GH, add sodium bicarbonate (NaHCO3), commonly known as baking soda. 1/2 teaspoon per 100 Liters raises the KH by about 1 dH. Sodium bicarbonate drives the pH towards an equilibrium value of 8.2.

What my experience showed was that adding 1/2-2/3 of a cup of crushed coral in a bag to the filter on a 45 gal. and a 50 gal. tank upped my KH abit but basically did not have any noticable effect on pH. My tests were done before the co2 system was installed.

[RTR]

Originally Posted by TwoTankAmin

RTR- I think that was the point I was trying to make. Lets assume one could set up two virtually identical co2 added tanks which had only one difference- one has crushed coral added and the other does not. All other things being equal, I would ecpect they would not give pH and KH test results that were identical.

Based on the chart on thekrib.com, I believe that for any given pH level, the higher the KH the higher the level of co2 will be. The converse is that at any given level of KH, the lower the pH, the greater the level of co2 is.

Yes, that is correct a quoted, but you are falling into un-justified assumptions again - the two tanks with different KH are not identical, for CO2 purposes, they are quite different. Plus you are falling into the fallacy of post hoc ergo propter hoc.. Supplementing KH does nor affect the readability of CO2 concentration via the KH/pH/CO2 relationship. It neither depresses nor enhances CO2 concentration. It makes the tank safer to operate without endangering the nitrification bacteria or risking pH crash, Supplementing the KH does affect the pH, and if you did not observe this, it was beyond the sensitivity of your observation or was accompanied by (but not necessarily causally related to the supplement) generation of sufficient organic acids to neutralize the effect. As you had stated earlier that your KH routinely declined between partials, i would expect the latter case to be the operative one.

Originally Posted by TwoTankAmin

My point is that the use of crushed coral, especially when it is a smaller amount that changes the KH levels a bit but barely moves the pH, the less reliable the pH/KH test for co2 levels will be.

First off, crushed coral is not the best agent to use, aragonite if better at it dissolved better at FW pH levels, but aside from that, if you used insufficient crushed coral to have the desired effect it is not something on which you would want to theorize concerning its effect on CO2 testing. But none the less, supplemented KH does not adversely affect the readability of pH depression by CO2. If you do suspect anomalous readings, the most likely issue is the assumption that no organic acids are present. That can be checked as outlined earlier in this thread.

If you do not assume no acids other than CO2 are present, and equally have no non-carbonate buffers added, the charts and graphs are quite useful, but both pH and KH measures must be current and accurate. The source of the carbonate/bicarbonate making up the KH is, for test purposes, completely trivial. If on a given tank (especially without CO2 supplement) the pH and KH do not agree in scale, there are obviously other factors than CO2 at work. Those factors do not include the source of the carbonate/bicarbonate's current KH reading.

HTH

[TwoTankAmin]

Perhaps I did not state clearly what I did. I knew I was about to set up a new tank that would be using pressurized co2 and that my tap water had a KH of about 5 dg. I also knew I did a 35-40% weekly change on all my tanks and would do so on the co2 added one about to be set up. As a precaution I wanted to be sure of what might be going on with the water params in my existing tanks in regards to KH levels. So I tested. What I discovered was the tank KH levels were consistently lower than my tap- as low as 2 dg. This indicated to me that without adding any co2, my tank KH was dropping over time- for whatever reason.

Therefore, as a precautionary/preventative measure I wanted to see what I could do to keep the KH levels higher. I decided to try adding some crushed coral in a bag on one of the filters on a 45 gal tank (the new co2 added tank was to be a 50 gal and I figured the 45 was pretty close in volume and had similar gravel and wood). After adding the coral I began to test the kh and discovered it climbed gradually over the next 2 weeks by about 2 dgs. However, the pH remained stable. This lead me to believe that a small amount of crushed coral would up the KH but would barely move the pH at all. Any more coral and I would have expected also to get a bit of a pH bump.

The upshot was I decided to add a similar amount of crushed coral to the Eheim on the new tank to help prevent any chance of a pH crash due to adding the co2. Once the new tank was up and running, I began a period of regular testing of the pH to determine how much the addition of co2 effected it. Tests were done several times a day in order to determine what change was happening and to determine what need there might be for dealing with nightime params with the gas running 24/7. I was prepared to outgas via an airstone at night if the need for this was evident from the testing. At the bubble rate I was running, there was not a huge pH drop overnight and I decided to allow the system to run 24/7 without any check on nightime rates.

The next thing I wanted to determine was what level of co2 was in the tank at the bubble rate I was running. For this I decided to try the pH/KH testing method and the chart posted above. And that is when I began to see unusual readings. I had planted a number of light loving, co2 needing plants, ones which would not thrive if nutrients and co2 levels were insufficient. In typical English garden fashion, I had overloaded the tank with plants which included rotala macrandra, ludwigia glandulosa, didiplis diandra. These plants did great, colors were vibrant, growth was rapid and pearling was ongoing- at times the tank looked like somebody had dropped in a couple of Alka Seltzers the pearling was so robust:



But when I began to test the pH/KH to extrapolate co2 levels, my results were indicating levels of about 14-15 ppm. But I also knew that this was an insufficient level for the results I was getting in terms of how the plants did. I expected to see something more on the order of 25 ppm or so. This is what led me to conclude that the addition of the coral and its effect on KH was throwing off the readings for actual co2 levels in the tank.

All this aside, as both a land and aquatic gardener I have always tended to rely on how the plants are doing as a guide to what I needed to add in terms of ferts etc. rather than using more technical methods of testing. I am an eyeballer more than "scientist".

[RTR]

There is absolutely no problem with eye-balling. Most experienced hobbyists use it the large majority of the time, and do so because it works. Novices don't yet have the educated eyes, so need alternate pathways.

I have only long-term operated one tank with supplemented CO2 where I needed to supplement KH (office 55, very different and much softer river-source water supply) I used a spare smallish external canister (Eheim adicts have spares). I used mesh bags of what was then Caribsea's coarsest aragonite substarte, with a bit of coral rubble added. The tank bags were traded out every few weeks for rinsing, drying, re-rinsing and back in to use. The aging reservoir bags were handled the same.

I had an office closet available, so was able to age my water there much as i do at home. Tap water was used to fill a caster-mounted Rubbermaid food-safe Roughneck with a circulation pump and glass strip with a heater for at least 48-72 hours, usually the full week between partials. There was a "blind" (unpowered) canister body in the circulation line, loaded with a similar bag of aragonite/rubble mix. This brought the partial water almost up to tank levels before it was used in the tank, and the small canister on the tank only had to bring the KH up a tab and hold it there. The tank was quite stable. Planting was quite heavy, but fewer stems than you use (lazy aquatic gardener). Lighting was staggered, moderate early and late cycle, only "high" for the middle half of the daily cycle Pearling was not obvious unless I killed the two internal circulation pumps just to show supersaturation.

As an aside, I am not a fan of 'effervescent' tanks. Oxygen saturation is certainly good and likely beneficial. Supersaturation and fizzy water bugs me. I am a current nut, so I am not generally bothered with excessive bubbles in the water column. But I am not convinced that I need high CO2 levels for pearling. Even my home, all moderate-lights tanks, do show pearling if I reduce the current, without CO2 supplement. But again, none of my plants require high light intensities or high nutrients for normal growth and metabolism. That is just not my personal style.