If your fish are truly creating too much mess and you're siphoning as much as you say you are, I can guess you're either
- Overfeeding
or
- Using white or light coloured small grained substrate
or
- Have many high waste producing fish
These options leave you with a few possibilities. I haven't seen what fish you have, or what tank dimensions you have, but if it really is that bad and you do siphon as often as you say you do, then perhaps change over to large gravel if possible? Or, upgrade to a larger filter, perhaps external?