gravel siphon

Hello, fellow Betta lovers! I have been searching for an answer to this question online, but I just can't seem to find a clear one. My dragon-scale betta is currently housed in a 2.5 gallon tank with decor, gravel, a tank heater and a thermometer; the water holds a 78-80 degree temperature at...

I just bought a small gravel siphon for my 2.5 gallon tank and it transports water fine, but it leaves all the gross residue and stuff. It just stirs it all up like a bowl of soup in my tank and then it settles back down, it doesn't actually clean out the debris. Am I doing something wrong? In...