Changing substrate and substrate Q's

[Friendlyfishies]

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 :) ...

[FishyFishy89]

If you have a sponge in your filter, that is where your cycle is kept. Not in your water. SOME beneficial bacteria(BB) has been known to be in your substrate, but your going to be keeping your current sponge media, so you shouldn't worry about dumping BB.