If it becomes a problem with your cat/cats getting up on your tank, you can get a special item called SSSSCat. It's a small can of compressed air (OK for the environment) that has an inferred top on it. When the cat (or anything) crosses the inferred, it let's out a blast of air. My cats know the SSSCat so well now that all I have to do is put a can down by anywhere I don't want them and they avoid the area. The compressed air canister are replaceable. The inferred top uses 1 or 2 AA batteries. You can order them on line. Here's a link, but I would shop around on the web for a better price.
http://www.entirelypets.com/ssscatinnotek.html
Also, I have used just a regular can of compressed air, like for computers and cameras, and without pointing it directly at my cat, let out a stream of air to get then off a table or away from something dangerous to them...again, after a while, just showing them the can makes them high tail it away. I like the compressed air better than a spray bottle with water, the air doesn't leave any mess and you can aim it towards pretty much anything and not worry about doing any damage. Of course, the regular cans of air can only work when you're around to supervise, while the SSSCat works all the time.
Just something to think about...
Ghpr1957