Why offer solutions when you don't have the water parameters? Without knowing the readings of his tank it's not simply safe to assume it's a lighting thing. He could be putting himself through mini cycles continuously. The green/yellow/brown/hazy look can all be affected by light or cause. A 90% water change may have just done a minor cleanup or algael water or just started yet another mini cycle. Giving tank information is very important to everyone if we are to help you rather than throw a million solutions at you. Water Temp, PH, KH, GH, Nitrite, Ammonia, Nitrate.... other things that will help, lighting, filtration, water change frequency, recent changes to the aquarium which includes new fish, plants, decor, etc. This will provide us with information that can be used to help you rather than having people randomly guess at what may be causing your problem. If you continue to experience your issues and would like to follow these suggestions, it may help to better diagnose your issue.