lol 20pd tank in 2 days?!? Its almost cool to hear you OD'd your plant on CO2 cuz i've never heard this before haha. But a plant is dying nontheless, sry man. I would be afraid to do Anything at this point including adding more nutes..what would TOO much CO2 do to a plant? Clearly(my guess) it has to come from where the stomata's are on the plant is my guess but what would actually be suffering from too much CO2/too little O2..idk man. Could you maybe find any grow information outside MJ forums about overdose of CO2? Would most likely coorelate to our plants. Hope you find help! PEace