You'll have to figure out how many times you want your tank to turn over. So judge your pipe size based on the gph
it's capable off and figure how many times an hour that will turn your tank over. Then you'll want to get a pump that is capable of handling that GPH
plus more. You'll always want an overpowered return pump. Things to take into consideration are bends in the piping and the distance and height water has to travel to return to the DT. Then when installing the return pump you'll want to include a ball valve in the return line to dial the pump to match the overflow.
In the most basic way of putting it lol. I'll see if I can find you an article.
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