Losing CYA

[OrangeAndBlue]

We're two months into our first swim season with the new pool and the summer heat has definitely arrived in Texas. I have been faithfully keeping up with the TFP methods and have had zero problems. However, now for the second time in a row I'm noticing a fairly significant CYA loss since my last full set of tests. I test FC and pH every 2-3 days, CC at least once a week, and everything else just monthly since I have realized that it has all been stable. I have to add some muriatic acid 2-3 times per week, but that's it.

I tested today (and re-tested just to be sure) and my CYA is at most 60, probably 50 if I'm really strict about not seeing the dot. One month ago at the beginning of May it was 80. At the end of April I had to add more stabilizer because it had dropped down to 60 from 80 at the beginning of April as well. That's two months in a row. I'm sure my margin of error for this test is at least 10ppm, but I assume my testing error is likely at least consistent and that would mean I'm losing 20ppm CYA or more per month. That's 3-4 lbs worth and seems like a crazy high amount to be losing per month. Any ideas what could cause this and how I could reduce it?

Few more details about the state of our pool:
I have been losing about 1 inch of water per week to evaporation and splash out, which I replace with both regular city water and softened / conditioned water at about 50/50. FC has been staying fairly steady around 5. Currently I'm achieving that with my SWG set to 80% running two 4 hour cycles per day (that's a daily FC demand of 2.5ppm if I used the SWG calculator correctly). Temps have been 90+ and sunny and our pool gets full sun through most of the day. I've been using the pool time brand stabilizer granules from Home Depot.

This afternoon's test results:
FC 5.0
CC 0
pH 7.8
TA 80
CH 350
CYA 50
Salt 3100
Temp 92F
CSI 0.13

 

[mknauss]

That is a bit high of CYA loss, depending on how much of your water loss is from splash out. Evaporation does not effect CYA.

I see about 10 ppm CYA loss during the summer months as we get hot (120+) and high UV sun angle.

I use the same CYA product. It is 100% Cyanuric Acid.

Take care.

 

[OrangeAndBlue]

Thanks mknauss. Even if my loss is all splash out, 1 inch of water should be in the neighborhood of 2-3% of my total pool volume. That doesn’t seem to be sufficient to even come close to what I’m seeing.

 

[mknauss]

Yes. But, my loss is entirely from oxidation. CYA does oxidize with strong UV impact. So the loss could be from oxidation and splash out.

 

[OrangeAndBlue]

So are you saying even 20-30ppm CYA loss in a month would be feasible with oxidation and splash out? And it's only the beginning June

 

[mknauss]

That much might be extreme, but 10+ is not out of the question.

Remember the test itself is at best +/- 10 ppm. You need to do the test in as close to the same environmental conditions as possible each time. Same time of day, full sun at back, etc.

Try using a different brand CYA. There have been reports in years past of some batches degrading more than others.

Take care.