Lisa,
I wish my valentines gift was a fish-tank. Unfortunately I got a new frying pan, a nice one, and a much needed one as the old one was knackered, but still nowhere near as nice as a fish-tank or two...
In motorsports there's a saying that goes like "You can't have too much horsepower". This can be translated into aquariums with "you can't have too much filter capacity".
I've got a RIO 400 [Birthday & Christmas present to myself] (but sometimes I wish I had two rio 180 instead... Maybe I will get another mid-size tank soon...). For my stocking, the filter seems fine (that's the Jumbo filter), but it's far from being at it's maximum stocking level with 6 Rosy barbs (about 2.5"), 5 Boesmans Rainbows (2-2.5"), 5
(~2") and 2
(2.5-3").
But if you build up the stock slowly, you should be able to check the nitrate levels. When the nitrate starts rising (after you've had the initial maturing cycle), you need to add more filter capacity.
Of course, for hypancistrus, you probably want some water movement to keep the fish happy too, so adding a filter rather than just a power-head might be a "kill two birds with one stone" approach.
--
Mats