Review on 🐠 Premium 2.6 Inch Dia Cylinder Pre-Filter Sponge Filter Media Pack - Ideal for Aquariums - Set of 6 Pieces by uxcell by Lori Williams

Fits aquaclear 50 inlet, although slightly loose. I bought these as a pre-filter and they work so no complaints. The rest is standard sponge. They could be a little tighter at the air intakes, but they're not made specifically for the AC50, so no big deal. Basically it stays on because it's wedged between the air intake and the rear window, but it definitely works because of the dirt I kept washing out while cleaning my filter. I highly recommend adding pre-filter sponges when using HOB filters as they prevent dirt from getting into the rest of your biocarrier, increasing the cleaning time for your cooktop and nearly doubling the biocapacity of your filters. Basically, it's like a sponge filter that then feeds your cooktop and all the bioenvironments it contains. Even in very densely stocked aquariums with plenty of food, my water parameters are optimal.