I was going to chime in my 2 cents worth also. If this is a s/w tank why are you using gravel?????? are you using crushed coral, if so I would highly suggest getting rid of it in favour of a deep sand bed with some good sand stirrers and you won't need to vacum it at all......it becomes a working denitrification factory. If this is a reef how are you emptying it with buckets? It sounds like what you have is a 75g f/w tank?? if so a siphon is the best way to go. ......