My fish (5 guppies, 6 pristella tetras and 3 otos in a 125l tank) seem to be entering a pooing olympic championship, and despite doing a vacuum and water change weekly, there seems to be a flurry of poo in certain areas of the tank. My gravel does not now slope smoothly from front to back as my gravel vaccuum disturbs the gravel quite a lot. Is there a simple way of vaccuuming this up wihout syphoning off too much water?! 
