I'm a total newbie and I'm having problems with my gravel vacuum. I bought a Marina Easy Clean self-starting vacuum (medium size, 16" tube) and tried to use it on my 6 gallon aquarium. I got the siphon mechanism to work, but it sucked up water only. I kept moving the cleaning tube up and down quickly trying to pick up the gravel (as illustrated in on the package) but the gravel didn't move up the tube very far (only about 2 inches) and it ended up just making a mess of my aquarium. All the fish and food waste spread into the water instead of into my bucket. Am I supposed to continue with the same rapid up-and-down movement once I get the thing started (the instructions weren't clear)? It really messed up my plants, spread waste around and was hard on my arm muscles. How frustrating! What did I do wrong? Is my vacuum too big? Please help!