CYA went from 30 to 40 to zero?

[Kelly Gordon]

A month ago, I got my first Taylor kit. Back then, my CYA measured at 30. A few weeks later, after using the rest of some leftover dichlor I had sitting around (in addition to the bleach I used to SLAM my pool), I tested my CYA at 40.

This week, I've slamming again. (Lesson learned: Don't let cool weather, rain and an auto cover fool you into neglecting the pool.) I'm almost done. My water is clear again, and while I haven't survived an OCLT yet, my CC is >.5. We're getting there. But just now, I tested my CYA, and it came in less than 20? I could see the dot fairly clearly even with the measuring area full of testing liquid. Is this possible? What's going on? PH is also low, at 7.0. I've never seen it that low in my pool. Last summer, I had to add muriatic acid every other week or so to keep it under 7.8.

The next wrinkle: I got a replacement cell for my SWG today. So I'm going to plug that in tonight too. Anything I should know as I transition from maintaining the pool myself with bleach for the last month to letting the SWG do the heavy lifting? Obviously, I need to get my CYA up. What else?

Kelly

 

[zea3]

Have you had a lot of water replacement due to heavy rain and backwashing? CYA test has a +/- of 10ppm accuracy, so less than 20ppm is not unheard of in those conditions. Keep testing the FC and dosing it daily until the SWG is able to maintain it at the correct level. It may take a couple of days for the SWG to catch up. Keep an eye on the pH as the SWG will cause pH to rise.

 

[Kelly Gordon]

We haven't had a lot of water displacement. Is the best route, then, to NOT add CYA right now and get the SWG and FC figured out? Maybe test CYA again in a week and make a judgement call about adding some then?

I'm guessing the same would hold true for the PH. If the SWG will cause the PH to rise, I should hold off on adding any sodium carbonate?

 

[zea3]

You want the CYA around 70 for the SWG, so once the slam is completed go ahead and add enough to reach 70ppm. As long as the pH is between 7.0-7.8 it is fine. If it gets up to 7.8 then you will want to bring it back down.