Here is the new design that I hope will keep my 125 RR going for some time.
As you can see I had to notch the tank out of bit for the thing to fit.
Had to cut the lids for the 5 gallons.
The water call fall out of the bottom
Foam on the bottom - stuff from an ac110
Then bio balls
Then filter material.
Then a plate to make sure the water goes all over.
Got 1 inch bulkheads for the top so I can slip the drains in and out.
Here is it with the stuff in.