I would go two SOW-15’s for a 75 gal. I have two in my 65 and it’s perfect. Two PP-8 isn’t enough flow if you want suspended waste (no dead spots) and if you want to keep acros. I am actually adding a SOW-8 (better than the PP series) to my 65 for flow for the backside of my tank. As for apex, I haven’t ever tried to tie in my jabeo pumps into it.