Basically the simple answer is; there is no "safe" level that can be applied to all tanks. It will depend on the type of fish species, other stress factors, age of fish, etc etc.
If you are asking "what CO2
level would you recommend", I can give you my answer of 20-30ppm.
Originally Posted by ringram
Most planted tank folks would say that 12ppm , in any situation, is too low on the Co2 scale. So, perhaps that just means that some fish aren't suitable for planted tanks (?).
You are refering to high light planted tanks only.
In nature, most freshwaters have a CO2
level of between 0-14ppm. You must remember that what we create with our high light planted tanks is not a representation of nature.... it is an accelerated ecosystem where we provide an excess of photosynthetic factors to try to obtain maximum or optimal growth.
Therefore one could argue that almost
no fish are "used" to living in water with a CO2
level above 20ppm, and they are in some way suffering in our home aquaria.
Unless major scientific research is done at this level of fishkeeping, we just cannot tell at present if, say for example 35ppm CO2
is long-term detrimental to x species of fish. (There's another experiment to add to the list Hoffboy!