CO2 testing - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 10-22-2009, 10:09 PM Thread Starter
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CO2 testing

Does anyone know of a commercially available test that will accurately determine CO2 levels in tank water??? I've used the KH vs. PH method, which seems unreliable, and the two agent Red Sea Fresh Lab Deluxe method (maybe I'm color blind, but the shade of the 10ml of tankwater is so pale I can't really tell when it changes from blue green to blue or blue/grey/pink). Does a reliable, accurate test exist (for less than an arm and a leg)? Also, am I to understand that too much CO2 can trigger algae outbreaks? My drop checker stays greenish yellow, my fish don't do any surface breathing, my plants are growing well, but I do have marginal algae issues (some green spot, some BBA). I really want to try to get the CO2 levels right, but without an accurate way to measure I'm not sure I can.

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post #2 of 8 (permalink) Old 10-22-2009, 11:15 PM
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Are you using aquarium water in your drop checker?

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post #3 of 8 (permalink) Old 10-23-2009, 07:54 AM
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i'm using a drop checker that i bought from ebay. it only has three colors and doesnt really offer much detail other than, "adequate co2, inadequate co2, and too much co2". but yeah i know what you mean, i once got a spike in my reading but figured later that it was because my co2 diffuser that was blowing bubbles in its general direction. anyway, i think to get a more accurate reading would require you to get a more detailed reading of pH so that you can reference it back to your CO2 reading, i mean 2 or more tests that have relevent readings make a clearer picture.
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post #4 of 8 (permalink) Old 10-23-2009, 03:10 PM
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The only accurate way to measure CO2 in water requires spending about $2000 for a special probe. That isn't justifiable unless you are doing lots of lab research where highly accurate results are required. We don't require that. You can do fine by letting the drop checker lead you to approximately the optimum amount, then fine tune it by increasing the bubble rate a little bit, watching the fish to be sure they don't all head for the surface to "gasp for air" or don't lay on the substrate, immoble. Then look for some pearling of the plants within a couple of hours after the lights come on. If you get the pearling and the fish aren't gasping, you are at the optimum bubble rate.

Unfortunately, that is only the optimum bubble rate for the present conditions in the tank. Once the plants grow a lot, their added mass means you need even more CO2, but their added bulk means it is much harder to get the good water circulation you need to get the CO2 evenly distributed around the tank. If you prune the plants well every week, this problem can be greatly reduced.

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post #5 of 8 (permalink) Old 10-23-2009, 05:47 PM
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I'm trying some things with an IR, but requires subsmapling and then letting the sample equilibrate.

PITA overall to test CO2 accurately.

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post #6 of 8 (permalink) Old 10-23-2009, 07:51 PM Thread Starter
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Quote:
Originally Posted by Left C View Post
Are you using aquarium water in your drop checker?
Nope- I'm using GLA's 4dKH solution.

As far as pearling goes, I'm having a hard time figuring that out. When I shut off my Koralia and the Eheim to spot treat the patches of BBA with Excel, many of the plants seem to behave like tiny airstones, releasing bubbles to the surface at a fairly steady rate; but when the pumps are on, the tiny bubbles of CO2 from the Hagen Elite Mini in-tank diffuser get blown all over the place and I can't tell the CO2 bubbles from the oxygen bubbles. I guess I'll maybe try doing my Excel treatment just a couple of hours after the lights go on to check for "pearling" earlier in the photoperiod as Hoppy suggests. What I'm wondering about is all the folks who cite actual PPM (30, 40, etc.) in their posts as if they have an accurate way to determine that- surely they don't all have the $2000 probe... And one more thing- I've read some posts saying that too much CO2 can cause algae outbreaks- but wouldn't you have dead fish first???
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post #7 of 8 (permalink) Old 10-23-2009, 10:12 PM
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CO2 doesn't cause algae outbreaks.

People who say they have 27 ppm, for example, of CO2 are fooling themselves. If they are using the KH/pH/ppmCO2 table, and they probably are, they very likely have a lot closer to 5 ppm than 27. Even the drop checker, which removes the tank water, with all of its various pH changing substances in it, from the equation, can only tell you that you have somewhere between about 25 and 45 ppm of CO2 when it is green. If you have any trouble distinguishing the shades of green apart, you won't even get that accuracy. And, that reading only applies at the position in the tank where you measured it, at the time that you measured it, so it is just a tool to persuade you to increase the bubble rate enough to get close to the optimum amount of CO2 in the water.

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post #8 of 8 (permalink) Old 10-23-2009, 10:34 PM
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Quote:
Originally Posted by comatoast View Post
Nope- I'm using GLA's 4dKH solution....
I was 99.999% sure that you were using the 4 dKH solution. It is the only thing that I could think of that could of been causing your troubles.

Would you want to try some 45 ppm solution from SuMo? I think that this is 6 dKH.
http://www.sumoregulator.com/DropCheckerSolutions.html

Toss that Red Sea CO2 test kit. It's worthless. I chucked mine away years ago.

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