CYA Disappearing

[mlaspina]

So, did a full test on Friday to open the pool side for swimming - we use the spa all winter long. Water was clear, but I noticed that the CL level seemed low considering I had set the cell at 100% on a 5 hour a day run. I soon discovered why: for the 2nd year in a row, CYA was zero. Added 4lbs to get it up to 40. Had to do the same last spring. What would cause CYA only to disappear over the course of a year?

My salt level is actually creeping up
My borate level is stable
My calcium is also creeping up (around 750 now - I'm in AZ, so 750 is normal here)

Other stats:
11k pool/spa combo, SWG, pebble sheen finish, cartridge filter

Everything I've read here says the only way to lower CYA is thru loss of water. I have no leaks, minimal splash out, and don't backwash. In addition the salt and borates are mostly stable (salt is around 3800 and it started at 3200 almost 3 years ago).

What could chemically be causing loss of CYA?

 

[Butterfly]

CYA is sometimes lost over the winter. It is believed that this is caused by anaerobic soil bacteria that can sometimes grow in pool water when the pool is covered and FC levels are zero.

 

[PSW]

Did you have a lot of rain this year? That is the most likely thing I can think of...as it would displace some of your water and dilute the CYA in your pool.

 

[mlaspina]

CYA is sometimes lost over the winter. It is believed that this is caused by anaerobic soil bacteria that can sometimes grow in pool water when the pool is covered and FC levels are zero.

Hmm - I could see this - it's pretty windy where we are. However, the pool is left uncovered during the winter.

 

[mlaspina]

Did you have a lot of rain this year? That is the most likely thing I can think of...as it would displace some of your water and dilute the CYA in your pool.

Much less then our usual paltry amount. I think like 2 - 3 inches since September. Anyway, that would not explain why the Salt and Borate levels are not dropping as well.

 

[duraleigh]

As Butterfly said, we have anecdotal information of CYA disappearing over the winter......it not uncommon enough to be called very rare but still unusual. It seems to occur in pools that are neglected during the winter and build up a lot of "junk".

In your case, it seems like your pools has been clear all winter and you have kept it clean, is that correct?

 

[mlaspina]

As Butterfly said, we have anecdotal information of CYA disappearing over the winter......it not uncommon enough to be called very rare but still unusual. It seems to occur in pools that are neglected during the winter and build up a lot of "junk".

In your case, it seems like your pools has been clear all winter and you have kept it clean, is that correct?

Yep - I check PH and chlorine weekly and sweep the steps once every week or 2 in the winter. Pool vac does the rest. Only seems to happen over the winter when the pool temp drops down.

 

[swimcmp]

I am in Missouri and we are just starting to ramp up on opening and almost all the pools we open are from 0 to 30 on the scale. Don't have an answer to why but I do experience the same thing here.

 

[ping]

This is interesting to me as I have had a similar experience with my CYA lowering during the winter. Last year, my first with the pool, I started with my CYA at 70 but was told to keep the FC around 1-3 ppm range. Come spring I found this site and learned my lessons in Pool School. My CYA had dropped to 30 and I wasn't able to hold my FC and was loosing more than 1 at night. Pool water was always clear and CC was .5, but I had to shock the pool for a week before the FC held overnight.

I also went through the same CYA loss this winter/spring. We use our spa on average 4 nights a week so our pool does have year round use. My SWG stopped working and I had to manually add bleach for about a month. The lowest FC reading that I got was 2 but I ended up having to shock the pool again to hold FC overnight. My CYA went from 70 down to about 35 this year. My salt and borate levels remained the same. I was using a cover when my CYA dropped and that is also when the solar was turned on.

Bump up your FC some and run an OCLT to see if you are holding FC overnight. My guess is that the FC got a little too low for the CYA level and the water had a low level algae problem that you could not see but was still there. The SWG is producing just enough chlorine to keep the algae from blooming but for some reason the CYA is lowered also.

 

[bk406]

I always end up with <20 ppm CYA when i open. whenm i closed last october, it was around 50. I opend last week and it was undetecable with the CYA test. My water was as clear as when i closed it. We had some rain over the winter, maybe 12 inches in the 6 months it was closed. I always open to low CYA.

 

[mlaspina]

I'll try the overnight test this weekend. Given the fact that the pool seems to be holding a much higher level after adding CYA, and there is virtually no combined CL, I would think that it would pass the overnight test. Time (and the test kit) will tell!

 

[Highlandreef]

Same thing here, got my test kit and tested the water
Came back less than 30
My Taylor 2006 kit doesn't read cya less than 30

 

[rcy]

Doesn't cold water affect the CYA test? With all these openings after winter, is it safe to assume that the water is much colder than when the pool was closed? Maybe the cold water is messing with the test results?

I drain below the returns for winter and the pool fills back up with rain and snowmelt through the safety cover over the winter. I always have low CYA because of the dilution with fresh water.

 

[Highlandreef]

I know when I tested it was nice out that day ~70.
I let the water from the pool sit for about 10 min then tested, I tested again cause at 1st the cya test came back low and was wondering if I missed something so ran the test again, the 2nd time I didn't wait and got the same results.
I remember seeing something about that on here but maybe chemgeek or someone will chime in?

 

[mlaspina]

Doesn't cold water affect the CYA test? With all these openings after winter, is it safe to assume that the water is much colder than when the pool was closed? Maybe the cold water is messing with the test results?

I drain below the returns for winter and the pool fills back up with rain and snowmelt through the safety cover over the winter. I always have low CYA because of the dilution with fresh water.

Not in my case - the pool was already in the upper 70s (we had 3 days in the triple digits this weekend), so I kicked the heater on to bring it up to 90 so the wife would go in.

 

[ping]

Doesn't cold water affect the CYA test? With all these openings after winter, is it safe to assume that the water is much colder than when the pool was closed? Maybe the cold water is messing with the test results?

I drain below the returns for winter and the pool fills back up with rain and snowmelt through the safety cover over the winter. I always have low CYA because of the dilution with fresh water.

I never close my pool and we only have had 6 inches of rain this year and my water is 80-85 degrees. I actually needed to add water this winter.

 

[Butterfly]

Doesn't cold water affect the CYA test? With all these openings after winter, is it safe to assume that the water is much colder than when the pool was closed? Maybe the cold water is messing with the test results?

Cold water can sometimes cause the CYA test to read lower than actual. The cold slows down the reaction, which can mean fewer of the particles that cloud the water are produced, the water is clear than it should be, and the reading is lower than actual.

 

[solarboy]

Just to chime in, I kept my pool open over winter with minimal loss of FC and left a few leaves in the bottom but nothing excessive. The pool wasn't covered at all. CYA was 80 at the end of last year but was practically zero in early May. The salt and borates level however were the same (2000ppm and 50ppm respectively).
I'm considering going back to trichlor pucks and sprinkling some leaves in the pool in the winter :lol:

 

[feetr2c]

For those of you just opening, is your water crystal clear yet? Cloudy water will falsely show a higher-than-actual CYA level since it uses the turbidity method of testing.

Sent from my MB865 using Tapatalk 2

 

[JasonLion]

For those of you just opening, is your water crystal clear yet? Cloudy water will falsely show a higher-than-actual CYA level since it uses the turbidity method of testing.

While this is possible in extreme cases, it is very unusual. If you have any doubts fill the CYA view tube all the way to the top with pool water. If you can see the black dot then the cloudiness of the pool water is not affecting the test results.