Thank you @Opae ula related; and yes it is a sponge filter. By the time I got advice to not put established freshwater gravel in the tank, I’ve already done so without washing the gravel and set things in. So I bought a filter to use for the first few weeks, and I turn it off at night so they get a break. I’ve also seen this particular sponge filter here in a thread when someone really wanted to put a sponge filter in here lol so I figured it would be fine.