CYA Loss

[ManiacalMama]

I wanted to see what everyone thinks of this, and if you guys think it's just normal oxidation of CYA or if I have something else going on.

I got my TF-100 test kit in May...CYA level was ~50 on 5/13
Fast forward to this month...about a little over a week ago I was sitting at just under the 30 mark. I retested several times, and even retested the next day from a different spot in the pool.

I threw 3 pucks in the pool (Leslie's jumbo tabs left over from previous owners) and I'm now reading just over 30 CYA.

Full test results yesterday A.M.-

FC 8.5
CC .5
PH 7.3-7.4
TA 90
CH 325
CYA >30
Temp 91

At one point I suspected a pool leak because I kept having to top off, but once usage from visitors slowed down and we kept the bubble cover on over a few days, the level didn't change, so I chalked up the water loss to evaporation and splash out.

Do you think the drop sounds like normal oxidation in those two months? A combination of oxidation and test variance?

I plan on bringing the CYA back up to 50, but just wanted to get your thoughts on this. Temps in this area have been highs in the upper 90's to 100.

Thanks All!

 

[mknauss]

I see up to 15 ppm CYA loss in June, July, and August. If you are well above your target level of FC that can be additive to the loss from UV oxidation.

 

[ManiacalMama]

I do keep FC a bit higher than target as we've been battling black algae. Hopefully we will be getting our pool replastered before next season and won't have to deal with that after this year.

Do you think the warm pool temp plays a part in CYA degradation too?

 

[mknauss]

It is believed to be UV impact, which coincides when the pool water is the warmest. Folks with heated pools in northern climates do not see our level of CYA degradation.

 

[ManiacalMama]

That's one thing that has me stumped, we have a blue bubble cover on our pool most of the time, only removing to either cool it down or to use it or for maintenance. So it really shouldn't get the full impact from UV, correct?

 

[mknauss]

True. Never thought of that ----

Degradation of Cyanuric Acid (CYA))

 

[JoyfulNoise]

Chlorine oxidizes CYA slowly over time. It increases when water warms up as the reactions rates double with every 13F increase in water temp. You see CYA oxidation most dramatically in a hot tub that is running their dichlor/bleach method of sanitation. Hot tubs see almost no UV light but the CYA levels will decrease quite steadily over time as the water is typically kept at 95-97F in standby mode and then increased to 104F when running the tub. It’s not uncommon to lose as much as 10ppm/month CYA in a hot tub. With a swimming pool, hot water and higher FC levels will result in faster CYA oxidation.

 

[PoolGate]

I lost 20 parts CYA from end of June to end of July (70 to 50). I keep my water in the 90s.

 

[borjis]

Every year I lose 20ppm of CYA between April and late May.

But it remains steady from July until the end of the season.

 

[ManiacalMama]

Thanks for all the responses, I'll stop worrying about it and just bring my CYA up a little bit.

 

[bizzle]

I just noticed a FC drop of about 2ppm and was trying to trouble shoot it until I thought to double check CYA and it's about 20 lower than last month's checkup. I hadn't been on top of it because I had read normal loss was single digits (and I started around 90 CYA).

 

[mknauss]

I just noticed a FC drop of about 2ppm and was trying to trouble shoot it until I thought to double check CYA and it's about 20 lower than last month's checkup. I hadn't been on top of it because I had read normal loss was single digits (and I started around 90 CYA).

Keep in mind, however, that out in the valley air temps are 110 right now and my *water* is 98F! I don't have a heater...do have a blue cover. I'm about to take it off during the day or during the night not sure which way to structure the blue cover to keep evaporation down but without turning my pool into a pot of stew

With that high of water temperature the oxidation of CYA is increased dramatically. I would suggest testing it every two weeks with those conditions.

 

[JoyfulNoise]

I would suggest taking the cover off the pool and leaving it off!! Your water temps are now right in the “Goldilocks zone” for bacterial and algae growth making your chlorine consumption a lot higher. If you took the cover off, you’d probably see about a 10F drop in water temp. Yes, your evaporation will go up and you’ll be topping off more often but that's the price for having a pool here in the desert.

 

[Arizonarob]

I just noticed a FC drop of about 2ppm and was trying to trouble shoot it until I thought to double check CYA and it's about 20 lower than last month's checkup. I hadn't been on top of it because I had read normal loss was single digits (and I started around 90 CYA).

Keep in mind, however, that out in the valley air temps are 110 right now and my *water* is 98F! I don't have a heater...do have a blue cover. I'm about to take it off during the day or during the night not sure which way to structure the blue cover to keep evaporation down but without turning my pool into a pot of stew

Why do you have a cover on it now at this time of year?? If anything, ditch the cover during the day to stop from heating your pool. Heck, ditch it all together so you can also get some cooling at night. Get some solar sails over the pool instead. I’m holding steady at 92 with the air being in tripple digits for weeks. Any higher, I’m gonna start tossing in tators & carrots!!

 

[bizzle]

I was getting bogged down with the science of it (leaving it off during the day or night comparing UV exposure to evaporation rate, etc.) and a newborn son!

 

[bizzle]

Why do you have a cover on it now at this time of year?? If anything, ditch the cover during the day to stop from heating your pool. Heck, ditch it all together so you can also get some cooling at night. Get some solar sails over the pool instead. I’m holding steady at 92 with the air being in tripple digits for weeks. Any higher, I’m gonna start tossing in tators & carrots!!

On a side note, this turned out to be a pretty (cost) effective way to reduce my CYA levels!

 

[ManiacalMama]

I'm actually not in the desert. I'm in the Central Valley. But even still...with blue cover on, UV oxidation should be minimal. In my case I can only figure that warm water temp, testing variation, and normal (highish) FC oxidation are the factors.