In part 2 of my under gravel filter series, I’m keeping it beginner-friendly and showing the basic way I get an under gravel filter tank set up so it actually works. The whole point is turning your entire substrate bed into your filter media—mechanical and biological—so you can grow a ton of beneficial bacteria right where the waste lands. That’s why I lean hard on fired clay substrates and volcanic rock/lava rock. They’re just awesome at hosting bacteria, and it’s a simple, old-school way to run a clean planted tank. I also own up to a major failure from part 1: I used a super soft “gardener” akadama that turned to dust immediately, and I had to strip the tank, pull plants, and redo the whole thing. Lesson learned—if you can crush akadama with your fingers, it’s not hard-fired enough for an under gravel setup. In this video I rebuild a 20-gallon high with a lava rock base layer over the plates, then a deeper mixed bed (fluorite, calcined clay, lava rock/eco-complete-style rock), add seasoned rocks and plant cuttings, and run a hang-on-back filter temporarily to clear the dust. About 45 minutes later it’s crystal clear, and I move my red dragon guppies back in with shrimp and ramshorn snails.