How do you determine CO2 levels if pH is lowered by driftwood - The Planted Tank Forum
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post #1 of 20 (permalink) Old 09-12-2007, 12:37 AM Thread Starter
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How do you determine CO2 levels if pH is lowered by driftwood

I am currently working on getting my pressurized CO2 setup going (just need a tank), and I am curious as to how I can measure the amount of CO2 in the tank if the driftwood is lowering the pH in the tank. Last time I checked the pH it was between 6.8 and 7.0. my kH is 4.5 and according to the CO2 chart on this forum I have above 12ppm CO2 which sounds wrong to me. I am just hoping to avoid a guessing game that may lead to a CO2 overdose and dead fish. Any help is greatly appreciated.
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post #2 of 20 (permalink) Old 09-12-2007, 02:06 AM
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A drop checker would work. However, you shouldn't use the aquarium water in the drop checker.
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post #3 of 20 (permalink) Old 09-12-2007, 02:27 AM
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^^ yup. Drop checker w/ reference kH solution.
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post #4 of 20 (permalink) Old 09-12-2007, 02:48 AM Thread Starter
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Alright thanks both of you, I guess I'll be ordering one soon.
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post #5 of 20 (permalink) Old 09-12-2007, 03:00 AM
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Paul,

I like using the drop checker (simple) with a known DK 4/5 soulution (using distilled H20) giving me a 30-40 ppm From all I've read...You can't KNOW your C02 ppm levels with your PH (ball park at best) due to uncontrollable variables (driftwood/Peat ect...,) Your own statement tells you that your base standard is suspect which will give you a varience... I do think that a PH controller would protect you from an overdose of C02... (empty tank surge)


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post #6 of 20 (permalink) Old 09-12-2007, 11:07 AM
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Maybe I don't fully understand how a drop checker works, but doesn't it just change color from pH? If that is the case, the user will be getting a false high reading due to the driftwood. Maybe the drop checker would still be useful if you use a lower "number" reference solution. I suppose you could take the pH of your tap water (that has been gassed out) and check it versus the tank's pH (without injecting CO2 for a couple days) . That difference should show you the effect your getting from the driftwood. Am I way off base here?


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post #7 of 20 (permalink) Old 09-12-2007, 12:23 PM
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Any buffers in the aquarium water never touch the reference solution in a drop checker, so the buffers are taken out of the equation.
A drop checker can work because CO2 goes into and comes out of solution relatively easily, and also likes to reach a point of equilibrium (where the amount in the water is at the same level as the amount outside the water). So the CO2 comes out of solution from the aquarium water in the airspace above the aquarium water, which in turn is absorbed into the reference solution & pH indicator reaching a point of equilibrium. The addition of CO2 will lower the pH in the reference solution, and change the color shown.

As far as a pH controller, please make sure you maintain your probe & calibrate the controller or you are asking for trouble. Also I know my water supply has had variances in the KH of my tap water making the use of a pH controller "wonky".

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post #8 of 20 (permalink) Old 09-12-2007, 12:31 PM
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You can also take a water sample, measure the PH. Let the Sample sit approx 24 hrs. Check the Ph again, a drop of 1 in Ph reflects 30ppm of C02.
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post #9 of 20 (permalink) Old 09-12-2007, 12:56 PM
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I don't understand why testing co2 the normal way won't work....In my understanding, driftwood drops pH by dropping hardness, including kH (If I'm wrong about this, then all bets are off). So, just test your kH and pH and it will tell you the co2. You don't need to buy a drop checker, although they are quite nice.

Why does 12ppm seem wrong to you? Are you sure your test kits are accurate?
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post #10 of 20 (permalink) Old 09-12-2007, 01:10 PM Thread Starter
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Quote:
Originally Posted by macclellan View Post
I don't understand why testing co2 the normal way won't work....In my understanding, driftwood drops pH by dropping hardness, including kH (If I'm wrong about this, then all bets are off). So, just test your kH and pH and it will tell you the co2. You don't need to buy a drop checker, although they are quite nice.

Why does 12ppm seem wrong to you? Are you sure your test kits are accurate?
12 ppm seems wrong to me because I am not injecting CO2 yet. If the average ambient level for regular water is like 2-5 dkh then 12ppm seems a little to far from that range. I am going to get some new kits and retest soon to make sure, but I think a drop checker would be an easy and accurate way to test my levels after looking into them some more.
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post #11 of 20 (permalink) Old 09-12-2007, 01:29 PM
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If your driftwood is leaching acids into the water, what will happen is exactly as you are describing, the water will test more acidic than it should be according to the KH. Driftwood will not remove hardness (KH, GH, or anything else). It's just adding acids which will mess with pH alone. The chart was not made to accommodate these types of variables, that's why a drop checker works best (using distilled water that has nothing in it to mess up the equation).

Also a drop of 1 pH when the water sits out will not necessarily mean 30ppm co2. It will mean that you have 10x the amount of co2 in the water before you let it sit out than you do after you let it sit out, but how do you know what you had originally? If you had 1ppm originally, then you have 10, but if you had 4ppm, then you have 40, so it's a pretty big margin of error there. It can tell you that you're doing something, but it can't really tell you how much.
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post #12 of 20 (permalink) Old 09-18-2007, 09:00 PM
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Quote:
Originally Posted by NwFishinfool View Post
You can also take a water sample, measure the PH. Let the Sample sit approx 24 hrs. Check the Ph again, a drop of 1 in Ph reflects 30ppm of C02.
Many use this method^. But its been said it takes more than 1 day for co2 to completely degass (unless perhaps you agitate it). I forget exactly, but think 2-3 days is more like it.
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post #13 of 20 (permalink) Old 09-19-2007, 12:59 AM
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a drop checker would be the easiest way. it would work independently of your tanks PH. i've always felt trying to figure it out co2 levels by calculating the tanks parameters proves to be inaccurate. the calculations do not take into account variables like surface agitation and buffers and etc... that are in your water.
a Dropchecker or a PH controller would do it for you accurately.


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post #14 of 20 (permalink) Old 09-19-2007, 02:22 AM
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I've got an auto pH rig but I buffer my water to 7.5 w/ baking soda. Does that mean that Chuck's calculactor isn't correct? ie... pH of 6.8 w/ KH of 7.5 doesn't necessarily mean CO2 of 36ppm? BTW, I've been told I'd be better off not to buffer and just go with my tap of .1KH and pH of 5.95 and set the auto pH to pH of 5. If that's correct, I'll gradually drop it w/ weekly 50% w/c's but it seems VERY low.
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post #15 of 20 (permalink) Old 09-19-2007, 03:29 PM
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Quote:
Originally Posted by Tdon1md View Post
I've got an auto pH rig but I buffer my water to 7.5 w/ baking soda. Does that mean that Chuck's calculactor isn't correct? ie... pH of 6.8 w/ KH of 7.5 doesn't necessarily mean CO2 of 36ppm? BTW, I've been told I'd be better off not to buffer and just go with my tap of .1KH and pH of 5.95 and set the auto pH to pH of 5. If that's correct, I'll gradually drop it w/ weekly 50% w/c's but it seems VERY low.
Well, why rely on just 1 method anyway? Its easy to set a cup of tank water out for a few days and then measure the change. Get a drop checker too, then you have 3 methods you can compare results with. Just a thought.
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