Big bud

the strategy behind a harvest flush is to essentially stress the plant in its final days for more trichomes production (the plant's defence system) - the key is to give the plant water with as low EC as possible (i.e. plain or RO water). So in your case, keeping the same water in the rez for the week or changing it daily should not have an impact on your harvest. Buds do not leach nutrients of them just because we are providing them with flushing water. Hope that helps - everyone is going to have an opinion on this subject :)