For a 90 gallon you'll probably want at least a 20 gallon sump in order to fit the required equipment. The more space you have to move around in the stand/sump area the better, otherwise it gets frustrating and overcrowded really quick. Remember that the sump is only about half-full, so you aren't actually adding 20 gallons to the system size.

I run my sump at about 3/4 to keep my skimmer operating at optimum. You should see how close it gets when I shut my pumps off! I've maybe got a gallon of wiggle room (if I'm lucky). I don't ever let hubby see that. :o

Haha, gotta love physics. It's a big puzzle of baffle heights, pump sizes and water flow.

Thanks_for_the_advice_on_the_sump..After_pricing_o ut_acrylic_I_have_decided_to_build_my_own_to_Maxim ize_sump_size..
The_other_question_I_have_is_should_I_go_duel_over _flow_in_the_tank??_one_on_each_of_the_corners??