On my old 125 gallon reef aquarium I designed my own aquarium sump. This aquarium sump is to house my protein skimmer, refugium and my return pump. The aquarium sump was located below the aquarium. I decided to go with a 55 gallon tank because they are inexpensive to find used and would provide enough space for a refugium, skimmer chamber and a return pump.
Picture of 125 gallon tank located in my bar
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The right chamber of the sump was where the drain lines came into the sump. The water then flowed over the glass baffle and went to the skimmer chamber. I used egg crate to build a riser for the protein skimmer in order to put the skimmer in the optimum water level. The next chamber was the fuge. It was light with a compact fluorescent light. The water then when down the angled slope through live rock to the return pump. I used a mag drive 12 pump for the return. The angled glass was used to reduce bubbles in the return. I never had any issues with micro bubbles.
Here is a picture of the sump in operation. It cost me only $75 to make and provided many years of operation without any issues.