Problems accurately measuring CO2

[exodus]

So I got the AP GH/KH test kit, along with having the Freshwater Master test kit. I'm trying to work out what my current CO2 level is, because im running at ~3-4 bubbles per second and I'd love to know where that puts me. Keep in mind, I'm running a high light setup with 2x 175 metal halides.

These GH/KH test kits suck IMO. The vagueness of the directions when it says "count the number of drops until it turns this color" couldnt be any worse if you ask me. Do they mean a hint of the color its supposed to turn, or brightly colored?

I just did the full workup on my tank following a few fish deaths, which im pretty sure was due to asphixiation again. About 2 months ago I lost 6 tiger barbs one night, woke up in the morning to find all fish gasping at the surface and the barbs dead with their mouths wide open. When I did a water change yesterday I found quite a few dead fish among the foliage; several neons, a GBR, my pictus cat, and my bala on the floor behind the tank most with their mouths open. grr. (I had been running the air pump at night on a seperate timer, but the timer stopped working and left the pump off for a week or so i guess, and this seems to be the outcome)

But back to the problem at hand. I did the full workup and got these results-

6 dKH
0ppm Nitrate
0ppm Nitrite
6.0 pH
0ppm Ammonia

...and I forgot to write down my GH reading. Darnit.

But if I calculated this correctly, my CO2 would be at 193ppm, which just doesnt seem accurate at that bubble rate, or considering the fact that im using a bubble "wand" as a diffuser.

Any idea what I'm doing wrong?

 

[Guest]

With my Kh test kit, I add one drop to the vial, and tap it slightly to mix. I do this with every drop until the color changes all the way(not partialy). The color will go from blue to completely un-blue. At your current Ph 6 and Kh 6, I show Co2 @ 180ppm which is high, according to Chucks Calculator. I guess the logical thing to do would be to cut back on the Co2 input.

 

[7Enigma]

So you are using the liquid AP pH test kit for your 6.0 reading? As you know it does not go lower than 6.0, so you could in fact be in the 5's. The bubbles per second is somewhat of a concern to get levels that high, but more concerning for me is the method of diffusion. A bubble wand unless extremely fine (like through an air stone) should not have enough time to fully diffuse the CO2 before the bubble reaches the surface. It does happen quickly, but if these bubbles are normal bubble wand size (pea size or slightly larger), you should NOT get this high results.

That and the fact that your bubble wand is agitating the surface of the tank which is increasing gas exchange, and something just doesn't make sense.

All that being said however, you most definately could be suffering from too much CO2 based on the symptoms you described. Gas exchange (both oxygen and carbon dioxide) in fish are passive. What that means is that they cannot have less CO2 in their blood than the water has (during exchange in the gills), and they cannot have any more oxygen than the water has. Because of this, when you have really high tank CO2 levels your fish will not be able to give off that CO2. Normal tanks with no CO2 injection are under 3ppm. That means in an ideal transfer that the blood at the fishes gills can approach 3ppm of CO2. Now your tank has closer to 200ppm of CO2. The blood at the fishes gills, AT BEST, can approach 200ppm, which is most likely much too high (i've heard anecdotal evidence that >100ppm and you risk losses).

But the diffusion method you are using, and the symptoms you are describing just don't make sense IMO. I'm wondering if there is another issue at work here. My best guess at this time would be not a CO2 poisoning, but more likely an O2 depletion at night when your plants and fish are using up the oxygen. Plants can survive low O2 situations, your fish cannot for long periods of time.

How well is your top sealed? Are you using a canister filter?

 

[Purrbox]

I would suggest checking your tap water (or whatever source water you are using for the tank) to ensure that the CO2 calculation is valid in your situation. Take a glass of the water and either let it sit for 24hrs or aerate it for an hour, then test for KH and pH. Your results should give you approximately 3ppm of CO2. If not there is something in your water that is throwing off the KH to pH relationship and you'll need to use an alternative method to calculate your CO2 levels.

If it turns out that the calculation is valid, then you are definately getting too much CO2 into the tank. You'll want decrease the bubble count until you get your levels back into safe ranges. You'll definately want it under 100ppm, and would be better between 30-60ppm.

Just one more thing that I noticed from your test results. Since your Nitrates have bottomed out your tank is primed for an algae outbreak. I would recommend increasing your Nitrate dosing ASAP.

 

[malkore]

I can totally see 3-4 bubbles per SECOND giving you over 100ppm of CO2. I run maybe 1bubble a second in a 75gallon tank widh a dKh of 10, and my CO2 stays about 40-45ppm.

The color change on the AP Kh and GH test kits is obvious. you MUST give it a good shake after each drop. it will noticably change from orange/yellow to blue (or whatever the colors are for the given test).

 

[exodus]

I'm gunna retest when i get home from work tonight. Until then, I turned my CO2 off, and I added an air line onto my power head last night so the fish should be happier. There's no way my CO2 could be that high..

I've been busy with work lately so I havn't been dosing my ferts, but on my way out I'll measure out some KNO3 and dose the tank. I have been noticing algae lately, but its been a lot worse in the earlier stages of the tank and as it matures its seeming like its going away. But I agree, 0ppm nitrates is no good at all.