aquaclear

I bought this catfish at my local Lfs and they sold it as a pimelodela cat but I’ve searched it up and my fish looks nothing like one. He’s a light grey and he’s about 2.5 inches, (I attached pictures of the fish)

So I have my new 75 gallon sitting in my room and I am letting the filter I bought for it (Quiet flow 55/75) run on my established 50 gallon which uses an aquaclear 50. my questions are 1. If I let the filter cycle and then attach that to my 75 along with many rocks, plastic plants, and gravel...