CYA Dropped on it's own?

[Queequeg]

Any idea what the water temperature is? Also, any idea of the typical FC level in the pool and the pH? Do you know the size of the pool in gallons? Does the pool have a sand filter backwashed weekly or a DE filter cleaned regularly (both of which would dilute the pool water)? Maybe the slow oxidation of CYA by chlorine becomes more noticeable at higher temperatures, but something still seems different here. Perhaps really strong sunlight also leads to some breakdown over time. We'll have to keep track of more pools to see if we can figure this one out!

My parent's pool? Here's my best estimate:

Temperature - Around 88-92F in the summer months, 60's 70's in the winter months.
Size - About 20,000 gal
They have a DE filter.

I wish I would have been testing my CYA more regularly so I could have tracked it as a function of Chlorine level and temperature. I tested it every week for the first couple months, but when it didn't seem to change (and I read that it shouldn't change) I stopped testing.

However, I do love a good mystery.

 

[branchop]

Actually Evaporation doesn't affect CYA like that. It becomes more concentrated, as the water evaporates. So say you have a CYA of 40....and 3 or 4 inches evaporates the CYA might increase slightly, hypothetically lets say 45, then you add more fresh water, which dilutes it, and puts it back where it was before, at like 40...

Draining, Splash out, or leaks reduces CYA. But technically, not evaporation.

I hope I explained that so it makes sense....

Seriously??? Then add me to the club of CYA dropping. Not as significant as a drop as 25, but enough. It was 50 at the beginning of the season and now it is 40. I chalked it up to draining rain water and replacing water when it evaporates. I really need to raise it about 60, but can't find the acid (and honestly haven't really tried - just occasionally) So I have bumped up the bleach per the pool calculator.

Sorry to have misled.

 

[Terry]

Add my pool to the list of CYA consuming pools. I offer the following as uncontrolled, non-scientific data. :-D

History:
Learned of cya/ chlorine relationship late May. Stopped using pucks and only using bleach since early June. Began testing cya in June, results consistently 100- 100+. My personal testing as well as pool store testing matched within margin of error. Began keeping a written log of results early July.

Early July added 160 lbs salt (no swg)

7/7 100+
7/8 100

Btwn 7/8 and 7/12 only chems added were 6% bleach (278 oz) and MA (170 oz) to reduce pH/ TA. Completed a reduction of TA from 120 on 7/9 to 70 on 7/11.

7/9 Drained 30% of water
7/12 Replaced 30% of water

7/13 70

7/13 Added borates. 836 oz Borax and 424 oz MA.

7/14 70
7/16 70
7/23 70

Only chems added btwn 7/14 and 8/1 were 6% bleach (2208 oz) and MA (24 oz)

8/2 Added ~ 20 lbs calcium

8/3 70+

NO swimmers between 8/3 and 8/13. NO backwashes/ vacuuming during this time.

8/13 50 Ran test 2x on 2 different water samples. Ran 3rd test 50% diluted w/ distilled water- result <30 (lowest reading on tube)
8/14 50 Ran test 2x on samples from different sides of pool.

Only chems added btwn 8/3 and 8/13 were 6% bleach (864 oz), MA (32 oz), and 32 oz DE (sand filter booster)

Pool temp has consistently been 86-88 all summer. Currently dropped to 84 due to a ‘less hot front’ that pushed through a couple days ago.

Filter runs 6 hours/day 2pm-8pm.

The pool has not seen any unusually high swimmer load, have not been gone on vacation, etc. Have not had any algae or CC readings since switching over to bleach. Pool crystal clear, no cloudiness. Testing w/ FAS-DPD, Taylor reagents.

Highest chlorine reading since I began record keeping was 15.5 (7/29) although this was 24 hours post chlorine addition and according to pool calc I should have been up to 20 ppm. Otherwise pool runs, on average, around 4-7 ppm.

I have logs of all tests ran/ chemical additions since July 6, however they are in a Word doc and I will need to figure out how to post them. If they would be helpful just let me know and I’ll work on that. It will be interesting to see what happens over time.

 

[frustratedpoolmom]

Seriously??? Then add me to the club of CYA dropping. Not as significant as a drop as 25, but enough. It was 50 at the beginning of the season and now it is 40. I chalked it up to draining rain water and replacing water when it evaporates. I really need to raise it about 60, but can't find the acid (and honestly haven't really tried - just occasionally) So I have bumped up the bleach per the pool calculator.

Sorry to have misled.

Draining off rain water would do it.... We had so much rain the last week or 2 that mine is down to 30....

 

[branchop]

We only drained about 2 inches - maybe. But we have replaced about a foot of water this season.

 

[nitz369]

Okay now someone is got me interested. I started my pool as a new pool owner in Feb, been using Bleach since day 1. I live in Las Vegas and water temp is generally 85-90 daily. I had huge chlorine loss and tried raising CYA to 70, tested it a week later and it was 70 on the dot. Tested today (approx 1 month later) CYA is about 25. I did just have a run it with organics of some sort since I went through approx 30 bottles of bleach to clear up the chlorine loss I was experiencing overnight.

1. Significant CYA loss
2. Extreme pool temps
3. TONS of Chlorine

I have another thread stated "BBB not for every state?" because I was questioning using it extreme heat locations. I can tell you that eveyrone around me and that I ever talk to has almost never has algae problems and uses pucks a trichlor consistently.

 

[chem geek]

In your situation, the combination of hot water temperatures and high chlorine levels may accelerate chlorine breakdown of CYA, which is normally slower. I can't explain the other people's situations with Trichlor. The higher temperatures would be a part of it, but unless they shocked their pools regularly at higher chlorine levels, I would guess that the lack of algae may have more to do with the luck of phosphate/nitrate poor water. Only time will tell as we get more info from a variety of users.