I don't vac the entire tank at once and you can do the same as long as the Nitrates are in check. My master kit has Nitrates in ppms, I test every week and they are consistently from 0 to 5. That is acceptable as long as the readings don't go to the end of the spectrucm. Once they start to rise I will vac half of the tank one weekend and the other half the next weekend. This will cut the workload down for you and will not obliterate your bennificial substrate bacteria, but this bacteria does recolonize quickly.