Help Me Please With Under Gravel Filters

I haven't used a UG myself, but I'm pretty sure you need to cover the entire bottom of the tank. I would go for a plate bigger than the tank bottom and cut it down. Be careful though as they can be quite flimsy.


Don't forget that UGs do have limitations. Real plants can clog the filter and the water flow can damage some roots. Large pieces of decor can create dead patches. You can't keep fish that like to dig in the gravel or they will expose the plate. And you need to avoid messy fish as lots of fish poo will just make a mess in the gravel.
Of course, you could use reverse flow pumps with a sponge prefilter which reduces the mess trapped under the UG plate and in the gravel.