I am just curious on peoples opinions. My tank has been cycling for 3 weeks now and am just curious as to when I do water changes, should I just replace the water, or should I actually dig into the substrate and get what I can from there, or possibly just skim the top of the substrate? I just didn't know if while the tank is cycling if I should leave all the stuff in the substrate or not? I am using a fish-in cycling with 7 zebra Danios on a 75 gallon tank. Thanks