We will not be using our hot tub for a period of just over 4 days and will not be able to add anything do it. I believe I've read that with no ozone and no bather waste to oxidize, the FC "should" drop about 25% / day. We have a Nature2 stick in the primary filter and 12 hours of filtration / day. Is it safe to say I should bring the FC level up to about 10 to last the 4 days? I wasn't sure if it was 25% of the initial each day (in which case I need about 12ppm on day 1 so there's about 2ppm left at the end) or if it's 25% of what's left so a 10ppm initial would leave about 3.2ppm at the end.