Wonderful fish cane. Instead of replacing all the sand with a fine gravel you could have removed most of the sand and leave a fine layer just barely enough to cover the bottom. This way it is very easy to clean and looks great. Many ray and discus keepers do this. Hows the cat doing?
Interesting that you changed the sand out because you didn't like it always looking dirty. Now instead of knowing where the dirt is and easily being able to get it (and having the impetus to get it) it can sink into the gravel and rot where you can't see it, or at least don't notice it.
I preffer to have the dirt where i can see it and syphon or net it out rather than have it sink into the gravel, unless you are a vacuming addict keeping the nitrates down with big fish and gravel is going to be a nightmare after a few months.
It also makes feeding harder on big cats and rays, gravel doesnt pass through the gills as well as sand which means the fish have to spit out mouthfulls of gravel before they can eat the next item
the tanks 100g and i have plans for it sorry.its either gonna house my 4 red bellied piranha or maybe a snakehead or i would love to try marine who knows