CYA too low?

[KatyO]

Need advice...

Second summer as a pool owner. We found out about the BBB method about halfway thru last summer and by that point the CYA was already in the 90s. Using the pool calculator and a complete test kit we had the pool sparkling all summer...even with the high chlorine demand.

Drained off a good bit of water for winter closing so I was hopeful that we could have a lower CYA this summer...and not have to keep the chlorine so high. Pool opened beautifully - balanced from day one. Never even had to shock it - passed overnight chlorine loss test from the start.

Current readings as of ten minutes ago
Temp 82
CYA 45
Ph 7.2
Alkalinity 70
Combined chlorine 0
Free chlorine 3.5 --------this is what I need help with! I can't keep the chlorine up in a decent range. Last night the chlorine was at 3 so I added a 128 oz bottle of 10% and a 128 oz bottle of 8.25% bleach....thinking that would bump it up to the top of the range and keep it in range for a couple days. I fell asleep before I could do a reading for an overnight test after adding the bleach...but as of tonight (about 24 hr after adding the bleach) I'm back to 3.5.

I'm going to add bleach tonight and do an overnight test again just to make sure something isnt brewing. If it is then I know I need to go through the shock process.

The thing is that the pool gets a solid 8-10 hours of direct sunlight everyday. Could it be losing that much chlorine just from the sun? If I pass the OCLT should I increase the CYA level? If so, what would be a good level to raise it to?

Last year we got to where we added one or two bottles of bleach about every third day....that kept things at the right levels. I'm currently having to add one or two bottles EVERY day. I'm not a fan of that!!

On the plus side the pool is gorgeous - so sparkly and clear. Not too shabby for a 15 year old pool!!

Oh I almost forgot - it's a 20x40 Grecian shape pool....best guess is 32,000-33,000 gallons. Vinyl liner. Haywood pump. Use a 380 Polaris to clean.

Thanks for any advice!!M

 

[257WbyMag]

Welcome to TFP!

You are going to need to do the overnight chlorine loss test to really know. After the sun is down, check your FC. Then, next morning before the sun rises, check the FC again. You should have lost no more than 1 ppm of FC over night. If you lost more than 1 pmm FC, then you are going to need to shock your pool.

 

[BoDarville]

KatyO:

Welcome to TFP

Your FC loss in 24 hours seems a little on the high side. If you started at 3 FC and then dosed according to your post, the new FC would be at ~ 8.7 ppm. After 24 hours, your FC was at 3.5 which puts your FC loss at around 60%. By comparison, I lose about 40% of FC on a clear sunny day at this time of year here in North Texas with the pool getting direct sunlight for much of the day and I'm running a CYA of 35-40 ppm.

I would do the OCLT as 257WbyMag suggested to rule out anything organic that could be consuming FC.

Also, what is the typical daily bather load of your pool? More bathers = higher FC consumption.

Another thing to check is to make sure there is no significant organic matter trapped in the skimmers or pump filter basket. That can act as a drag on FC consumption.

After checking all of the above, you may need to increase CYA slightly. All other factors equal, the amount of CYA needed to combat FC loss will differ based on your location. Pools in more southerly latitudes will generally require more CYA than pools in the north. If you increase CYA, I would do it very gradually. When your FC consumption drops to an acceptable point, then you have found the sweet spot for your pool.

If you would, please put the city and state (or country) in which you live in your profile or in your text. Your climate is important to the advice you receive.

 

[KatyO]

Okay - morning update.

Passed OCLT. About 45 minutes after adding a gallon of 10% bleach last night I tested and FC was 7.5. This morning it was still 7.5.

My husband is really good about keeping the skimmers and Polaris bag cleaned out - so I don't think it is organic matter eating up the chlorine.

As for bather load - it is actually pretty low. The day that I mentioned in the post where it lost so much FC we didn't do any swimming at all. We swim more on weekends and maybe in the evenings for a little bit.

We live just outside Little Rock, Arkansas.

If I am going to increase CYA - what is the best method? I saw hth "Balancer/Stabilzer" at the store - the ingredients listed CYA as the only active ingredient. What's this sock method I see people referring to?

 

[Richard320]

There are pictures of the sock method in this thread i-m-new-here-but-i-ve-been-reading-everything-i-can-t59801.html Old nylons work, too. You could also tie them to an empty jug or a pool noodle or something and just let it float around until it's all dissolved, but the pummeling from the return speeds it up.

 

[KatyO]

Thanks!!!!