A new test?


Prolific Poster
May 18, 2005
Hi Tom and others,

I did a search, but couldn't find the answer to this question. Maybe it has been talked about and I have just forgotten......

What happens to plants when there is too much CO2 in the water? Say double to triple the recomended amount 60-90pm. With the advent of the 4/5dKH drop checker method we should be able to easily target these amounts.

Have you done this experiment for an extened period Say 1-2 weeks? I remember reading several times that CO2 over 30ppm doesn't improve plant growth but will too much CO2 (lets say the ranges mentioned above) actually hinder plant growth/hurt the plants?

For all intents and purpose lets make this a fish free tank so as to not upset animal lovers with the thought of killing the fish.

Thanks for any insight,

Ken T.

Tom Barr

Staff member
Jan 23, 2005
If you remove the fish etc, then adding a lot more than 30ppm is not going to increase plant growth, even at high light levels, which can also reduce CO2 uptake if excessive(seldom the case for us, even with 1000w MH's: 800micromol vs 2000 (full sun).

Some plants might do better etc but most should be fine.
We generally add more till no new increase in growth rate is noted.
You need non limiting conditions for the other parameters.

I think you might be able to hinder plant growth at extremely levels, 500ppm etc.

An interesting tidbit is the resistance to diffusion of CO2, this goes back to the CO2 mist issue.

You can increase the CO2 delivery to a submersed plant without having to dissolve the CO2, leaving it instead in the gas phase where it can break through the leaf's boundary layer and supply higher concentrations rapidly to the plant.

Tom Barr