The only reason my system works is I change water. If you don't have plants to remove the nitrates and phosphate, the system will eventually become un-usable. I end up dumping about 100 gallons every week. I'm very much looking forward to aquaponics grow beds. Once these are cycled I can stop dumping the water and I won't need the sand filter. I will keep the aquacube though. It isn't practicle to move enough water through the beds to keep up with the ammonia. 50 GPM is a lot of flow, but that is what is needed in an intensive system to keep up with it.