depends on how you do the water change. Lets just say you did this, clean the sand and rock a bit with all the pumps off, then take a submersible pump and stick it into the tank and turn it on. You can get a pump of any size and just pump the water right out into a drain with waterever your using. Then do the same process to fill it back up with premixed SW. I might use a different pump but using the same one wouldnt hurt you either lol. May sound like a lot of stuff to get, but sounds like this would work well one would think.