Frag tanks

[clayjay144]

I am starting a 30 gallon frag tank I'm getting a plain 30 gallon rectangle aquarium for 30 bucks I have lights and I'm raising the frag rack with PVC up in the air my only setback is a filter I thought about gluing in a piece of acrylic making it like the back of a biocube but don't know how thick it should be since its inside an aquarium and also what are some other options