pulled the cover back last week and tested my water before adding anything, which i'm glad i did. cya came back at 110 ppm, which i wasn't expecting since i drained about a third of the pool last fall. been running the pump with no chemicals while i figure out how much i need to dilute before i can even think about shocking it. anybody else dealing with high cya at opening or is this more of a mid-season thing from overusing stabilized chlorine tabs all summer?
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first opening this year and my cya is already off the charts
- Thread starter NC_Nick
- Start date
Kind of in the same boat right now, though my cya was only around 80 when I tested last week. I thought draining a third of the pool would have brought it down more than that, so your situation makes more sense to me now - sounds like the starting level was really high before the drain. From what I've been reading, once you're up at 110 you basically have to dilute significantly before chlorine can even do much, so I get why you're holding off on shocking. Do you know roughly what level you're trying to get down to before you start treating? I've seen people say 30 to 50 is the target range but I'm not sure if that changes depending on whether you're going with tabs or liquid.
Same thing happened to me two seasons ago. I was at 90 after what I thought was a meaningful partial drain and figured another third out would get me close enough to work with - it did, but I had to top off slowly to avoid thermal shock issues since my well water was cold. At 110 you're probably looking at draining closer to half before chlorine even starts doing real work.
your math on the drain actually checks out, nick. if you drained a third and refilled, you'd expect roughly a 33% reduction - so if you ended up at 110, you were probably sitting around 160-165 going into fall. that's not uncommon if you were using trichlor tabs all season, since each pound of tabs adds about 6 ppm of cya on top of the chlorine. it stacks up faster than most people expect.
for where you are now, i'd plan on draining closer to 40-45% before you bother shocking. at 110 ppm your free chlorine demand goes way up, and you'd need to hold fc somewhere around 15-20 ppm to get meaningful sanitizing against algae. that's expensive and hard to sustain. once you dilute down to the 40-50 ppm range you'll be in a much more manageable spot. if your fill water is cold like nroberts mentioned, drain slowly, refill slowly, and keep an eye on your heater settings so you're not stressing the shell or equipment with a big temp swing. test again before you add anything, because fill water chemistry can throw off your baseline more than you'd think.
for where you are now, i'd plan on draining closer to 40-45% before you bother shocking. at 110 ppm your free chlorine demand goes way up, and you'd need to hold fc somewhere around 15-20 ppm to get meaningful sanitizing against algae. that's expensive and hard to sustain. once you dilute down to the 40-50 ppm range you'll be in a much more manageable spot. if your fill water is cold like nroberts mentioned, drain slowly, refill slowly, and keep an eye on your heater settings so you're not stressing the shell or equipment with a big temp swing. test again before you add anything, because fill water chemistry can throw off your baseline more than you'd think.
Nick, I'm kind of in the same situation as you but earlier in the process so this thread is really helpful. Quick question though - when you say you drained a third last fall, did you do that all at once or spread it over a few days? I ask because my neighbor told me to do it gradually to avoid messing with the ground pressure around the walls, but I'm not sure if that actually matters or if he was just being overly cautious. Also I didn't even think to test before adding my spring chemicals last year, so I basically have no idea what my cya was going into winter. Definitely writing that down as something to do first this year before I touch anything.