I have 2 emperor 200's hanging on this tank....Was thinking of adding a marienland 360c canister.....Will this combo be plenty or will it still be cutting it short?
It depends on stock....Oscar Messy... Filter more , a school of Tetras less....
get the picture...
the GPH rating is basically without or Clean Filters...so typically in order to get the BB you don't change the media just rinse with Tap.
For a 90 I would have gone with 2 Emp 400's
If you can add the canister that should give you plenty.
IMO with a stocked tank, you should be around 10x gallons per GPH.
So you should be over 900 gph total in say a slightly overstocked African Cichlid Tank.