My girlfriend and I did a substrate change with the fish still in the tank and now the water is very cloudy and dark. I advised her that I didnt think it was good to change out the substrate with the fish still in the water but, she has more experience in aquariums than I do so I agreed. The substrate we used was colorquartz T grade. Now I look at it I am not so sure it was a good idea. Do you guys think it will affect the fish? I am new to this hobby so I have no idea but i cant imagine the cloudy water being good for the fish. 