Thank you for the response. So you filled up DT into the overflow or stop b4 the overflow? Sorry, it just seem daunting coming from sumpless also lolHi. I used to have a sumpless tank. It's a big difference to have a reef ready tank. So much fun. I filled up the DT first. Turn off all pumps to see where your water level and start from there so you won't have any flooding issues.