Amount of light filtration reducing light wavelenghts for plant growth will depend on: 1. the darkness of the tannin, 2. the filtration ability of tannin to selectively filter wavelengths needed by plants mostly green plants. Some good homework may provide your answer. I have nothing for you. Please share your research.
I do know that when the addition of new tannin subsides the tannin will gradually and naturally be reduced.
Last edited by Bill Cody; 01/17/17 09:01 PM.