You cannot keep goldfish without filtration. Goldies expel and enormous amount
of ammonia into the water. Your fish are swimming in their own waste, and will
eventually be ill. You don't say how small the tank is, but rule of thumb is
10g per fish. You can get an Aquaclear 150 for a 10g tank and keep 2 fish,
because it's over filtered (I know, because I've had to do this for about a
year), but you also need some kind of bubble bar or other aeriation.

Don't over wash the gravel (I could be wrong, maybe you're not supposed to wash
it at all, I use sand) because the gravel contains the bio-bugs - benficial
bacteria - to keep the tank healthy.

I don't know what a water hoover is, unless it's a python, but that's just a
modified syphon hose.

You need to do a litte research, goldfish can grow over 12" long and live over
20 years, they need lots of space. I have a new 150g tank for just 6 fish.

Deanna