Welcome to the forum,

You didn't mention the size of your pool/fish tank.

I don't know why you think you need a sump. Just drain the grow bed back into the fish tank.

With the grow bed/bio-filter size you mentioned, you can raise 10 pounds of fish before it overwhelms your bio-filter. You will need a minimum of 6 gallons of bio-filter per pound of fish when fully grown out.

Flood and drain cycle time of every 15 minutes is about right. Your drain time seems fast for a constant input flow grow bed. I'm wondering how you accomplished that.

Oliver