CYA level dropping

[rosensama]

I added 3lbs of CYA granules to my pool this spring to bring it up to our target of 70ppm, confirmed by testing. I just measured again today because chlorine demand was high and it has dropped to between 0 and 10. My understanding is that the only way to lower CYA is to empty and refill with fresh water. I've been backwashing and filling the pool the usual amount so there's no way I've cycled more than 80% of the water these past few months.

When I first measured I thought my reagent must have gone bad, but the pool store measured the same.

Is there anything else that could account for the disappearance of CYA?

Thanks,
Rob

 

[chem geek]

If the pool got to zero chlorine at some point then there can be a bacterial conversion of CYA into ammonia or nitrogen gas. Could that have happened?

The other possibility for degradation is if you had the chlorine level very high for an extended period of time, especially at higher pH. This could happen with a SLAM, especially at yellow/mustard algae levels. Could that have happened?

 

[jaduck]

Hello! Can you post a full set of results? How old are your reagents? Is your pool crystal clear?

 

[rosensama]

If the pool got to zero chlorine at some point then there can be a bacterial conversion of CYA into ammonia or nitrogen gas. Could that have happened?

The other possibility for degradation is if you had the chlorine level very high for an extended period of time, especially at higher pH. This could happen with a SLAM, especially at yellow/mustard algae levels. Could that have happened?

Yes, some of these have happened since I added CYA this Spring. Occaisionally I'm a slacker and the chlorine goes to zero. Also my pH tends to drift up over time and during those same slacker times can reach 8 or so. I have shocked once this year, but not to mustard levels, unless my CYA had already fallen.

- - - Updated - - -

If SLAMing at high pH can lower CYA levels, that might be preferable to replacing water. Particularly for those in drought struck areas. Any reason that's not recommended?

 

[rosensama]

Hello! Can you post a full set of results? How old are your reagents? Is your pool crystal clear?

Hiya, my TF-100 is about 10 months old. Today's tests tied out with the pool store, so I assume the reagents are still good. Water is crystal clear.

pH: 7.6
FC: 1.0, seeing it low this morning made me do the full test because I measured 8.0 after adding chlorine Thursday evening
CC: 0
TA: 80
CH: 325
CYA: <= 10, I just added some this afternoon and will measure again tomorrow afternoon

 

[chem geek]

If SLAMing at high pH can lower CYA levels, that might be preferable to replacing water. Particularly for those in drought struck areas. Any reason that's not recommended?

Because it's not consistently reliable, is a rather slow process, and the high pH needed can lead to metal staining or scaling especially in pools saturated with calcium carbonate such as plaster pools.

 

[Scoop]

I was curious last summer about CYA depletion rates so I began tracking it when I discontinued using Trichlor Tablets and began using the TFP methods with Bleach.

DATE CYA
06/18/14 95
09/02/14 75
11/10/14 55
11/22/14 55
01/19/15 55
03/11/15 55
04/14/15 35

The approx. depletion rate was around 10/Month last summer and about 3/Week from March-April 2015.

No depletion occurred between November and March.

I added liquid CYA last month to raise the calculated value to ~60-70.

I'll see if I get the same consistent depletion rates as last summer.

 

[shacke]

I'm having similar issues with cya dropping and I have put plenty in this season! I know it isn't supposed to really go away but it does. I'm afraid to put in even more in case it's a false reading but I use the tfk100 and it's just me doing the test.

How long before the reagent might be bad??

I should say my chemistry is solid otherwise.

 

[AprilsZoo]

Scoop,

Would you say that the changes are what you would expect given gradual dilution due to water replacement after backwashing, accounting for splash/drag out, vac-to-waste (if applicable), &/or rain overflow? Essentially, any water additions that weren't to top-off after evaporation?

I think I'll start trying to track how much water I add, and when....

Anyone know if there's some sort of gadget that can be added between the spigot and hose to measure how many gallons are "dispensed" (for lack of another term...)? And what it's called, if it has a name?

Thanks.

 

[AprilsZoo]

I thought that CYA reagent couldn't really "go bad"...

Once upon a time, I asked at TFP's older, frequently nameless, but not forgotten, "stepbrother" site and I'm pretty sure it was ChemGeek who told me that melamine (CYA reagent) is very stable, and would be good to use indefinitely if I kept it indoors, in a dark, cool location.

I hope it keeps, because I bought 16 oz. and still have at least 2/3^rds of the bottle left.. It cost about the same as a couple of the 2 oz. bottles, so I'm sure I've "gotten my money's worth," but I'm a little OCD about being frugal.

 

[Texas Splash]

Hey Rob, along with what Chem geek said, also remember all of our rain earlier this year. I know my pool overfilled several times requiring me to constantly drain excess. My CYA dropped quite a bit causing me to continuously add stabilizer My CYA was down to about 20, and I am currently soaking yet another sock to get back to 60. The rain was tremendous this spring, so that may have accounted from some of your loss.

 

[Scoop]

Scoop,

Would you say that the changes are what you would expect given gradual dilution due to water replacement after backwashing, accounting for splash/drag out, vac-to-waste (if applicable), &/or rain overflow? Essentially, any water additions that weren't to top-off after evaporation?

I think I'll start trying to track how much water I add, and when....

Anyone know if there's some sort of gadget that can be added between the spigot and hose to measure how many gallons are "dispensed" (for lack of another term...)? And what it's called, if it has a name?

Thanks.

I'd say you're right, for the reasons you mentioned. In addition, I backwash with 10 backwash/rinse cycles which removes a significantly larger portion of water than normal evaporation.

During that time when the CYA was dropping about 10/Month, I backwashed once.

The interesting part of the backwash theory is that, during the period of time that my CYA didn't drop, I backwashed twice.

I'm wondering if this is a natural effect of seasonal change, the sun's angle, cooler temps, etc. , since it was the winter months in Dallas when the CYA level stayed at a constant 50-55 .

I'll know more after I track a 2nd summer/winter season of CYA levels. I'd be lost without my Excel file :lol:


Here's an Amazon link to one type of garden hose water meter. I think that's what you were asking about.

P3 P0550 Water Meter

 

[rosensama]

Hey Rob, along with what Chem geek said, also remember all of our rain earlier this year. I know my pool overfilled several times requiring me to constantly drain excess. My CYA dropped quite a bit causing me to continuously add stabilizer My CYA was down to about 20, and I am currently soaking yet another sock to get back to 60. The rain was tremendous this spring, so that may have accounted from some of your loss.

Yeah, I had thought of that, and it must have contributed. Say we got 30 inches since I last added CYA and it all mixed in really well and overflowed. That should be equivalent to replacing 40% of my pool water. Add in maybe another 15-20% due to backwashing for 4 months and at least we're in the ballpark of the drop I've observed.

Anyways, it's good to know that CYA does leave the water in other ways than water replacement. I'll make sure to measure monthly now and not assume it's exiting at a constant rate due to backwashing. It also makes me more comfortable throwing in the pucks when I go on vaca.

 

[chem geek]

Chlorine slowly oxidizes CYA. Usually it's around 2-3 ppm CYA per month in pools and 5 ppm CYA per month in hot spas. Perhaps more exposure to sunlight accelerates its degradation. Scientific papers such as this one and this one describe why CYA, unlike most organic compounds, is resistant to breakdown from hydroxyl radicals. Resistant does not mean completely immune, however. So it is possible that when chlorine breaks down in sunlight to form hydroxyl radicals that it accelerates the breakdown of CYA and the second paper showed that hydrogen peroxide in sunlight (which produces hydroxyl radicals in the water) did break down CYA. However, we don't see this consistently in all pools exposed to sunlight so there may be something else in pools with higher CYA loss rates.

We have seen that chlorine loss rates in sunlight are higher than explained by the unbound chlorine (hypochlorous acid and hypochlorite ion) so as I describe in this post, this breakdown might result in creation of a partially oxidized CYA which would not fully show up in CYA tests and may not bind to chlorine as strongly (not sure about that, however).

Note that the lack of CYA breakdown during the winter months could in part be due to lower temperature so slower chlorine oxidation of CYA and less sunlight. However the change of rate was rather dramatic. The solar insolation for Houston (Dallas wasn't listed, but would be similar) is the following in kWh/m²/day by month.

Jan ... Feb .. Mar ... Apr .. May .. Jun .. Jul ... Aug .. Sep ... Oct .. Nov .. Dec
2.47 . 3.50 . 4.40 . 5.59 . 6.03 . 6.45 . 6.36 . 6.07 . 5.46 . 4.61 . 3.30 . 2.44

 

[Scoop]

chem geek

Thanks for the info.

I tested my CYA a little while ago and it hadn't dropped since my last test on 07/01 . I'd expected to see a drop of ~10 based on test results since last summer.

We're having a typical summer in Dallas, around 100-103° for the daily high temps right now with little to no rainfall recently in the area.

I'll test again in a month.