CYA levels keep declining...

[lvrpl]

I'm a bit stumped on this one and was hoping for some help. We replastered the pool and filled it about 40 days ago (just bought the house and immediately did a replaster). At that point, I added enough stabilizer to get the CYA up to 40 (per PoolMath). Two weeks later, CYA measured in at 20. Again, I added enough stabilizer to get it up to 35 or so. A week later, it measured at about 25. I added enough stabilizer to get it up to 35 again. Today it measured at a bit over 20, maybe closer to 25.

What on earth could be causing my CYA to continue dropping? We do have an automatic filler on the pool, but I rarely if ever hear it on, so I can't imagine it's auto-filling and draining the water constantly. Also had one big rainstorm which might explain one of the drops, but not all three. (Also, before anyone says I should have been targeting a CYA of 50 and not 35, I agree - I'm going to be out of town for 7 days in a couple of weeks so I was keeping the CYA lower so that I could use some pucks then and end up at a CYA I like).

Any thoughts what might be going on? I thought CYA could only go down if water were rained and refilled. Thanks for any help.

 

[woodyp]

Your auto fill may be compensating for an auto-leak you have someplace.

 

[Texas Splash]

Curious, do you remember what brand stabilizer you used previously? I had a similar problem with HTH.

 

[BuckeyeChris]

I lose about 5 ppm per month, just using pucks yo bring it back up every so often. I do suspect there is a supply chain foe these various products that is putting out cya that doesn't behave as expected, just based on reading here.

 

[lvrpl]

Your auto fill may be compensating for an auto-leak you have someplace.

Possible, I suppose. Any easy way to determine if I have a leak?

- - - Updated - - -

Curious, do you remember what brand stabilizer you used previously? I had a similar problem with HTH.

It was HTH. First bottle was purchased from Walmart, current bottle is from Home Depot (but I haven't used much of it yet). I'll try something else next. What brand did you switch to?

 

[JVTrain]

Easy way to determine if you have a leak is to turn off your auto-fill, then do the Bucket Test. This is just putting a bucket on your steps or other solid feature that will keep at least some of the 5-gallon bucket above the pool water surface. Put a rock or other heavy object in the bottom of the bucket then fill the bucket to the same level as your pool. Wait a day or longer and if the water level in the bucket is higher than the pool, you have a leak.

 

[pooldv]

Turn off the water supply to the autofill to see if the water level drops too much. Also, if your chlorine level spends much time below the minimum level then bacteria can grow that will consume CYA. Chlorine CYA Chart

 

[Texas Splash]

FYI - I also got my first bottle of HT from Wal-Mart - lasted about 1 month then CYA started to drop. Tried a brand called Aqua Chem, and that seemed to hold a little better. Just bought another bottle of HTH from Home Depot about a week ago - waiting to test my CYA again after a week of dissolving. Kind of makes you go ... hummmm?

 

[lvrpl]

Easy way to determine if you have a leak is to turn off your auto-fill, then do the Bucket Test. This is just putting a bucket on your steps or other solid feature that will keep at least some of the 5-gallon bucket above the pool water surface. Put a rock or other heavy object in the bottom of the bucket then fill the bucket to the same level as your pool. Wait a day or longer and if the water level in the bucket is higher than the pool, you have a leak.

How much of the loss would you expect to be from evaporation? That's definitely at play here in DFW.

 

[jblizzle]

My odd experience for CYA was also using HTH.

 

[Crackerjack4u]

I've had really good luck, and good holding of my CYA level with the Step 1 Clorox Chlorine Stabilizer Brand that I purchased from Lowes.

EDIT: I'm really glad to read this because I certainly won't be getting the HTH brand because it looks like several of you folks have had issues with it.

Lvrpl- If you have any left in the jug I'd take it back to Walmart because it doesn't work like its suppose to. If you have your receipt they'll give you your money back, if you don't have your receipt, they'll put the return amount on a gift card. That stuff is Not cheap, and nothing makes me any madder then spending good money on a bad product.

 

[Sparkle]

CYA measured in at 20.
A week later, it measured at about 25.
Today it measured [...] maybe closer to 25.

What on earth could be causing my CYA to continue dropping?

~20
~25
~25

From what you're writing, you have not measured a CYA drop.

Also, the TF-100 test kit measures CYA in tens if you follow the directions included with the kit.

How much of the loss would you expect to be from evaporation?

You don't lose CYA to evaporation. So measured CYA should increase as water evaporates, then back down as you add water.

 

[jblizzle]

Yeah those test results are in the noise. Mine dropped 30ppm in a month.

 

[BuckeyeChris]

Does cya have a shelf life degradation that we know of?

 

[chem geek]

Kept cool and dry it has an unlimited shelf life.

 

[lvrpl]

~20
~25
~25

From what you're writing, you have not measured a CYA drop.

Also, the TF-100 test kit measures CYA in tens if you follow the directions included with the kit.

Sure, I guess I'm saying there's an implied drop because I've been adding CYA but the level isn't going up.

Also, the TF-100 test kit measures CYA in tens if you follow the directions included with the kit.

Fair point - I guess I'm interpolating a bit because the CYA test is relatively more tricky. I did it 3 or 4 times, it kept coming out somewhere between 20 and 30 on the TF-100 view tube (sometimes closer to 20, sometimes closer to 30). Also, I ordered and used some of the 50ppm CYA solution just to calibrate myself and make sure I'm looking for the correct "disappearance" of the black dot.

You don't lose CYA to evaporation. So measured CYA should increase as water evaporates, then back down as you add water.

Understood - my question about evaporation was actually referring to water in the pool and the bucket leak test JVTrain referred to above. However, you are pointing out why I'm confused on my CYA levels - it's not lost to evaporation, so where the heck is it going? Sounds like it's either a leak (which I'll check, but I honestly think is unlikely) or something is consuming/breaking down CYA (which I previously didn't know was possible, but sounds like it might be).

My understanding before had been that CYA levels basically never change unless there is some water drained and refilled, sort of like CH. Sounds like it might not be quite that simple?

 

[chem geek]

CYA slowly gets oxidized by chlorine, but this is not seen over days or a week but rather over months. The loss rate varies but is around 2-3 ppm CYA per month though some people see 5 ppm per month and we've had some reports of 10 ppm per month though that might be from other causes not yet understood. In hot spas the typical loss is 5 ppm CYA per month. Doing a SLAM will increase the rate of such losses, but usually a SLAM doesn't last for a month.

 

[prs]

I use BioGuard brand CYA purchased from my local pool store, addition amounts and test results pretty much line up with PoolMath. I try to maintain a CYA of 80, and see zero loss of CYA over the winter months. During the summer, with our endless days of full sun, daytime temps around 100°F, and pool water temp over 80°F, I see CYA losses between 5 and 10 ppm per month.

 

[BuckeyeChris]

so... who wants to set up two different buckets of tap water and add HTH vs Other cya and test the results?

 

[zamazing]

My odd experience for CYA was also using HTH.

Has anyone used this brand of CYA from Backyard Pool Superstore? http://www.ebay.com/itm/291511544549?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT They sell on both Amazon and eBay and their prices are pretty low.