I've added my two cents in this thread LOL.
I think ballincrew is right, just go slow and adjust as needed. I have my overflow as low as it can go adn have the water about an inch over the top of the plastic. If the power goes out I have enough room in the sump for the water plus I have a hole drilled in my return pipe near the water line AND a check valve so no water gets back siphoned from the output hose. I run a very tight margin for my overflows cause I'm super paranoid about it flooding.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.