Ideal Co2 Concentration

[PrettyFishies]

Hello all,

I have a 20 gal tank with the following:

KH 4.5
PH 6.8
GH 15

Co2 - 22 ppm
http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

QUESTION:

What's the ideal concentration? That page says 10-25 and that 25 ppm can be harmful to fish. I've seen 30 ppm as a reccomendation. Thoughts from experience?

 

[Purrbox]

That page has a much more conservative recommendations than commonly found now. Now you'll most often find that 30ppm is the recommended target. It's also been determined that CO2 doesn't become harmful to fish until the concentration gets above 100ppm.

 

[PrettyFishies]

What's the REAL difference between 25 and 30ppm from the plant's perspective? Do different plants need different concentrations?

 

[Hoovercat]

Like almost everything else in this part of the hobby, there are many schools of thought. Some say AT LEAST 30ppm, some say AT MOST 30ppm. In reality it's very unlikely you'll have 30ppm at the point your calculations show it to be. Personally, I tend to err to the high side of the scale. It won't hurt to have 45ppm but plants won't benefit. Your fish won't suffer in the least.

To directly answer your question it's a common notion that 30ppm is the highest level of CO2 plants can benefit from. Someone else may know of a particular specie that can use higher levels but it will likely be a "weed" that uses it to take over your tank.

 

[Purrbox]

Actually the main difference has to do with algae and not the plants. You are less likely to run into problems with BBA for example if you CO2 levels are at or above 30ppm.