im not sure how much extra space i need for the backflow but the way i see it i left about 2 gallons for backflow. if the pump cuts out the tank will just fill up all the way. or most of the way depending on the amout of overflow from the tank. the water level should just leve out due to preasure from the incoming water. the water flows into the first chamber then underneath to the protein skimmer then back up into the next chamber which creates even flow to the fuge area. it has to flow from the protein skimmer chamber into anothe chamber is that it would not have evin flow in the corner next to the intake chamber. so i put up a secound wall just lower then the wall leving the ps chamber.
35 gallon hex salt water tank
4 in. sand bed
berlin air-rise proteine skimmer
. wisper power filter
1 damsel, 1black urchent, 1 arrow head crab, 1 red baned shrimp, 1 coral banded shrimp, 2 peppermint shrimp, 1 sandsifting star, 3 mexican tubo snails