I have a baby Alligator snapper in a 20 gallon tank with only half of the tank full. I want to change 50 percent of the water twice a month and vacuum all the gravel once a month. I am using the python syphon kit that connects to the sink, but when I am vacuuming the gravel, it ends up taking out most of the water. Am I doing something wrong or can anyone give me any advice on your water change routines and what equipment to use during the process?? Thanks!