You don't need a "high power" vacuum. All of them are powered by the water flow when you remove the water from the aquarium.
When I clean the gravel, I have to push the vacuum down to suck at the gravel. The gravel might get sucked up a little (depend on how big they are), but they should fall back down before being completed sucked away. At the same time the fish waste and other debris should be removed.
Unless of course, your vacuum is too tiny. Even if it is small, you should use the vacuum to dig around at the gravel in order to remove the debris.
Actually you might as well just go to a local store to pick up one. I got mine from a local walmart.
You only need to clean the gravel once a week during the weekly partial water change. As long as you do not overfeed, your filter system should handle the ammonia produced from the fish waste just fine.
