Danny
HYDROS Expert
If you are using the Hydros AWC regimen you want the return pump to run while it does the water change since that uses the same sensor as the ATO to refill so you want everything to run like it is normal. That means it will limit the amount of the water change each time. I do three water changes a day. A small amount each time. I use dosing pumps for ATO and AWC and the drain pump currently runs for 10 minutes each time but the pump has a flow rate of 60ml a minute so that would be 600ml each time. It is only a 42 gallon tank.