We understand you are fish only, but LR is so much better of a way to go.
The sump can be most any size.. and it can be of something that will fit your space.. the shape and method is numerous .. to whatever fits. The main idea is to have an overflow.. you have been doing that to run a canister.. and tank of some shape that can house cheato to grow with a strong cheap light. That way algae nutriments are consumed in the sump and less in the tank.
Then you stop buying filter media.. and let nature do what it does best.
There are plenty of members on here who can take you through at baby steps. Some forum members use containers they got at wallymart for their sumps.
Will a 10 gallon tank fit in the cabinet?
Those are frequently given away at garage sales or nearly given away. One pet shop chain sometimes has aquarium tanks on sale for $1 per gallon during promotions.
How was the water moved into and out of your canister?
Pictures will help loads... we really WANT to help... we enjoy it.
Look around in the DIY section to see what you can find about home made sumps here in this forum. Here is the link: ......
Do It Yourself (DIY)