Ok,
We have 125 gl tank with a sump. I bought it used off CL. It used to be a salt but I house a BIG pacu in it. He was bought 15 years ago by my unknowing hubby. When we married 3 years ago I took over his care.
(lack of) he was in a 55 gl, so thick with algea you couldn't see in. He ate all his tank mates because he was being fed flakes. I'm not sure how the fish survived honestly.
So, the tank has a sump (with a pump that we just replaced yesterday) It ran off a Walmart filter and water Changes for the last 5 weeks after the old pump went out.
Be has been in this tank for about a year. A serious upgrade for him but I still don't know if I'm doing it right. It's been trial and error.
Pacu (Big) 3 clown loaches, 1 pleco, 3 silver dollars, 2 algea eaters, 5 tetra barbs and a black catfish. He has not harmed any friends in the New tank 😃
I struggle with high nitrates. Even with adding prime. I guess he poops alot.
The sump has bio balls, fluval rocks and a nylon sponge on top. The pump is a reflo snapper or dart.
What else do I need to add or do? There are spots to add accessories but I don't know what.
I'll ncluded pics of the setup, if I can figure out how.

Thanks, angela