yea i dont think 1 tsp/gal of gro big would do that to bigpot. First see if overwatering is he prob, which it kind of does look like. Maybee if its not overwatering and lowering the lights doesnt get his leafs standing up, I may think about throwing some mycorrhizal fungi on top of the soil b4 ur next watering. It is used to stimulate root uptake of nutrients, u can get it at ur local indoor gardening store. All u do is sprinkle it on top ur soil b4 u water and it seeps down into the roots. If that doesnt help then im not too sure. Sorry i cant b of more help