to be on the safe side,i say 5,but only because some weeks are easy,some are a little more difficult.i will give an example,i had my kribs for a year and half,no problems,happy,healthy,then one day i notice lavernes colorings not right,wilder tells me it's septicimia and tells me what meds i need so i rush out and get it and then have to play the waiting game.is she going to be alright,is she going to die,i had to treat her for 2 weeks and thanks to wilder she is back to normal.my point is that sometimes it's easy,how hard it can be depends on how much you care about your fish.