I want to change out the substrate in one of my tanks and add more substrate to my other tank...I want to use sand of course ...to make this more comfortable for the fish, should I put half of the current tank water in a bowl, dump the rest, toss the substrate then add the new sand then add the old water from the bowl? I dont have a cycle yet, so I dont think anything will mess with the cycle but I just want to keep my fishes less stressed ...