A faster way to do this is what some people call a "peat bomb" . Take a section of 4" pvc with screw on caps and plumb a power head to push water through the pipe . It can be used in a holding tank or plumbed right into a supply line to your holding tank without the pump. A few discus keepers used to do this a few years ago. The screw on caps allow you to easily change out the peat.