chem geek said:
That's interesting Tim. This does seem a bit higher than usually seen, especially at the higher CYA level. So do you bounce between 10 ppm and 6 ppm or 9 ppm and 6 ppm FC or something like that? What is the depth of your pool, both shallow and deep ends (if it has both)? Your loss with the pool covered is exceptionally low. In my pool if there is no bather load and the pool is covered the daily chlorine use is around 0.7 ppm FC per day, but this is at warmer 88ºF temps. If the water gets closer to 80ºF then the chlorine usage drops considerably by almost half.
I originally had my CYA at around 45-50 (I'm never
quite sure where that dot completely disappears. If I stare at it long enough, it often seems to come back.
) and I was losing about the same amount at 75 degrees. I ramped the CYA up to try to lower the demand, but at the same time the temps went up, so it stayed roughly the same. My 0.5ppm/day loss with the pool covered is actually a few weeks old, when the air and water temps were a bit cooler. DW and kids use it fairly frequently, but not every day. I haven't had it covered for a week at a time since the beginning of May, so my current demand in that situation may be a bit higher right now. If it stays covered for a day, I often won't test that day, since I know it's not going to drop below my minimum level.
Yes, it's bouncing between 10-6 or 9-6. In a purely unscientific observation (not even a deliberate test,) over the past couple of days, I raised FC from 6 to (supposedly) 10 on Monday at around 4:30 pm. Left the pool uncovered until about 6:30p (about the time the sun went behind the house, and the pool was in full shade.) I covered it, and it remained covered all day Tuesday and again all morning and early afternoon Wednesday until about 3:00pm, when it is still in full sun. During that time, we got about 1/8" rain, and a couple of worms in the pool. (I still want to know how I get worms in an above ground pool. I've even gotten them with the winter cover on, so it can't be birds!) At 8:00pm, Wednesday, FC was back down to 7.0. The water temp at that time was 87. That drop seems to be bit high for having the pool uncovered only 7 hours and only 1/8" rain, but I've never tried to keep track of how much I lose during any given time. (i.e. so much from 6am-9am, so much from 9am-12pm, etc.) It's still only a 3ppm drop over more than 48 hours.
I'm using WalMart "Great Value" 6%. I have no real reason to think it is incredibly old, since they do go through a lot at the store. On the other hand, I'm basing my upper level on the amount I've added - its been a while since I actually tested after adding bleach to see what level I'm really hitting. It's possible that I'm off a bit, but probably not much. The last time I tested after adding, I was off by less than 0.2ppm. I do actually measure the amount I'm putting in using a graduated pitcher marked off in pints, so I'm always within a couple of ounces of my target. According to the pool calculator, in my pool 1 quart of 6% is a gain of 1.1ppm, and one gallon is 4.6ppm.
I don't have a deep end, but the center (round pool) is about 2" deeper that the sides. The sides are normally about 47" and the center is normally about 49". We've had several inches of rain over the past week, and I haven't drained it back down yet. Between rain, evaporation, and splash out, my net water gain over the past couple of weeks has been 2-1/2", so I'm a bit high right now. The FC demand has remained pretty constant since the beginning of May. If the pool is uncovered, the demand is going to be between 3-4ppm/day. If the pool is covered, it's significantly lower.
I've done all my calcs on a uniform depth of 48". It's been a while since I actually measured the depth, but it's pretty close to that.
I also don't have any reason to think I have any organics beyond the occasional bug or worm, since my FC loss with the pool covered is so low. The water is also very clear, so no indication there. I haven't actually done an overnight test, simply because I haven't had any indication that I need to. I probably should, just to be sure.
To help on the amount of jugs folks are lugging an alternative is to switch to 12.5% liquid chlorine or get a swg.
