CHOMPERS;3026858; said:Looks like a winner.
You think

You just missed the two most common standard designs when making sumps

No1 Not a good idea to have your media in the up flowing chambers of the sump it’s a real pain. It tends to end up flowing over into the next chamber or you are always trying to keep it down.
No2 Not a good idea to have your media all the way to the base as this will cause poor water flow through your media (dead spots) as pointed out by roadk1. It’s very simple to stop just place some egg crate or smiler material at the base so there is a nice gap at the bottom for better water flow check new sump design out below.
I know you are on a budget but bio-balls are not meant to be submerged. Pot scrubbers are cheap and make a very good bio media but if that’s all you got then use them .
Better option