It maybe good for fish that need acidic water and yes it could control the PH.

However it is totally going against what a plant need the most in the root zone 02. The green of the plant needs the c02 and from what I have heard it is not a good idea. Of coarse there is always some one who tries it. It would be interesting to know for sure if you have a grow you can take a chance on killing.

I think I would go with the auto PH system. It works the same way with a constant meter and a tank of PH up and down.