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I've never really tested my co2 level, I always thought if the fish gasped at the top then that is too much and just done it a bit less than that. I have a PH monitor and they gasp around 6.0 so I keep it around 6.1.

How important is it to be near 15-30ppm, and how do I test it? I'm going to be doing the PPS pro method very soon.

I've always thought of co2 to be beneficial, and not really a problem, but I'm starting to think that maybe too much gas could have led to my plants having problems?
 

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Testing CO2 directly is difficult to do accurately.

Better to rely on the gasping fish to tell you when there is enough CO2.

You can also use the KH-pH relationship chart to figure out approximately how much CO2 is in the water. The results might be off if there are other acids or buffers in the water though. Its best to run a separate test on distilled water with a known pH and KH to make sure your tank values are accurate.

Do a google search for "pH-KH CO2 relationship," tons of good info on it out there.

Too much CO2 can cause a problem, not because it takes O2's place in the water (because even with crazy high CO2, there will be the same O2 levels), but because with so much CO2 around the plant's receptors are occupied by it for a majority of the time and don't let the O2 in the water into the plant.

You actually can't lower the pH of water below about 4.5 with CO2, water reaches its saturation point around 4.5 and can't dissolve more. CO2 is just not that strong of an acid.
 

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It depends on conditions in the tank. If there is a lot of dissolved O2 as well, temperatures are cooler, lots of water currents etc... the value will be different.

I estimate that if the pH is below 5.5 then you probably aren't helping the plants out by adding so much CO2. On the other hand you might not be hurting them by that much. There is a gradient with everything, a little too much CO2 might not harm the plants by that much.

There are lots of other factors to think about. The monetary cost of keeping the CO2 levels low, the stress it causes fish and other tank inhabitants (snails, bacteria, etc...)

I think keeping the CO2 at around 6 is fine.

Have a look at the CO2 calculator half way down the page at http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

Allow for some error in the calculation since there will undoubtedly be organic buffers and acids in the tank.
 

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Figuring out the exact CO2 level in your tank is a bit difficult. If you go here you can find a way to do it:

http://www.aquaticplantcentral.com/forumapc/equipment/59274-how-set-up-your-co2-controller.html

It's not necessary to find the exact level of CO2 in your tank. You have the basic idea about decreasing pH until you stress the fish. I would try string at a higher pH and going down slowly. I've found the even before your fish start gulping for air they begin to become less active.

You should have a drop checker in your tank to monitor the CO2 level in addition to your CO2 controller.

I'm not sure what benefit there is to high CO2. At 20 ppm where I keep my tank the plants grow way to rapidly doubling in biomass about every 2-3 weeks.
 

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Discussion Starter #6
Thanks for all your replies. My tap water comes out around 7.4-7.5, I've reduced the level of the bubbles (which was uncountable before) to around 1-2 bubbles a second.

My KH 4, so it goes a bit off the richter scale on that calculator. I do however have problems with phosphate normally, I've just added some phoslock in there to reduce, seems to help the plants when I do that.

My fish don't really move around much when it's 6.0-6.2 they seem a bit lazy, but flying all around the tank at 6.5 which it currently is at the moment. I'll see how the plants fair in the next two weeks.

This drop checker how accurate are they by the way?
 

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A drop checker is really only a ball park estimate based on color. When there is no CO2 the checker is blue. When there is way too much it is yellow. god is some shade of green based on your tank and fish.

Once your tank is set it; if the color of the checker doesn't change and the pH doesn't change everything is Okie Dokie. If the color changes or the pH changes something is out and you need to recalibrate.

BTW the checker is fairly slow to react so it takes a few hours after you put it in the tank before it comes to the eqilibrium color.

BTW2 Your plants should be pearling (ie giving off O2) with the extra CO2. This is usually a sign that they are doing well.
 
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