Same setup but I only use 20gal of water for 1 4x4. I've done it 2 ways, first was 20 girls in 6x6 cubes with hydroton filled up around it. Worked great but the clean up after was a pain. Second was the same way but no hydroton which I made a few mistakes by not letting it fill up at least 3/4 of way of the tray. So I switched to 6" baskets with hydroton inside the baskets along with 3-6"x3' water bags on the sides of tray. Now with a 20gal res it fills up in 5 minutes up to the top of basket. Also make sure your overflow valve is higher so it take longer to fill up. Like anything else, its trial & error & works for some & not others.