DIY 15 or 20 gal AIO idea

A few days ago I was gluing some zoos in my old acrylic eclipse tank, talking and not really paying attention, and the glue got on the front of the tank and the attempts to remove it have left the tank looking pretty bad...so time for a new tank! I decided to do an AIO tank and attempt to do it myself, for some fun, but I'm not sure if my idea would work, so I'll ask you all to see what you think.

Here's an overview pic of my sketchup:



I have an 18" T5 fixture, which I know isn't much light, but it serves my purposes well, so I want to keep the display tank around that size, so after all is said and done I think a 20H or 15L would work well.



The water goes into the overflow area, and I was thinking about putting a little rack in there for some purigen or charcoal or something, then it would go into a small refugium area, I'd keep chaeto and some rock in and light with a 13 watt PC over top of it that I have left over from the eclipse. The only problem I see is water movement in this fuge space, and I'd have to come up with a way to fix that--any ideas??



Then it would go into the return chamber and a a hydor pico evolution 1200 or a powerhead or something would pump it back into the display tank.

So, any input would be greatly appreciated!
Thanks!