I don't know
Originally I had my sump configured like this:
Flow to the refugium was supplied by teeing off my returnline and directing some of the flow back into the fuge. It was a good theory but it never worked right. I think the size of the fuge was too large and the current was lost.
Just the other day I decided to switch the fuge and skimmer chambers around and added a powerhead. The flow from the powerhead is just off center and it creates a whirlpool effect. I also thinned out the macro and this helped too.
Tinker tinker tinker - That's all I know. The rest is up to the aquarium gods.
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