Keep needing to add CYA - why would this be.

[wayner]

Thanks - I did just get a Taylor kit and I tested myself and got <30 of CYA. In past years I have never had to add more than about 1.5 kgs of CYA. This year I have added about 4.5 kgs in the last month, and also another 1.5 kg in May when the pool first opened. The last addition was 1.75 kg yesterday in socks at the pool returns - this has now all dissipated into the pool. Unless anyone suggests otherwise I won't bother testing the CYA for another few days as it seems to take several days to properly dissolve and the Taylor kit that I bought has enough reagent for about 6 CYA tests.

But why have I needed to add so much? There hasn't been a ton of splashing out as the pool hasn't been used that much this year.

I know people don't trust pool shops but my pool shop appears to have been pretty good. In past years my main issue was not enough CYA early in the year and after adding some they generally said everything was good.

 

[duraleigh]

Wayner,

Check your PM's.

 

[wayner]

I tested late last night about 6 days after adding 1.8kg of CYA. The CYA test sample is now a bit cloudy and I would say that the level is about 31. So last night I added another 1.8kgs of stabilizer (it dissolved quite quickly in a sock - less than 3 hours for the whole amount). According to PoolMath that should bring my CYA up to about 50 as it appears that 1.8kg of CYA raises the CYA by 20 for a 100,000L pool. That would also imply that my CYA was 10 before the addition of 1.8kg a week ago. But then what happened to the other several kgs that I added earlier this year and the residual CYA from last season? FYI this latest addition was a different brand - it was GLB.

 

[duraleigh]

FYI this latest addition was a different brand - it was GLB.

That seems like a variable that has changed....I would stay with GLB and never look back.

 

[wayner]

Although the previous bottle that I added a week ago was not GLB - it was the same stuff that I had been adding earlier in the year and it raised the CYA from <30 (aka too low to measure since I can still see the black dot clearly) to 31. The GLB was what I added last night.

 

[toofast]

Funny...I have a very similar issue...and you are in the same general area as me. I wonder if the super cold winter had some other chemical effect on the water, as it seems there is more than one person having issues getting CYA to build.

I ran at 30 all last year with a covered pool and rock stable....this year I started with 0, added enough to get to 50, only tested at 40 and now my 40 is 30

I've added some more, but only time will tell. I honestly think quite a few of us have some wacked out issues that are unexplainable, and I wonder if all of us went through the super deep freeze.

 

[engrav]

subscribed as I too have CYA dwindles not totally resolved and the outcome of this thread may be helpful

jblizzle reports the CYA test is ± 15 and Isaac-1 ± 10
not sure if this is over the entire range, from 0 to 100 or where and
probably does not matter if CYA is 100

but if CYA reads <30 your actual could be 0 to 45 as per the above which would be Ok

if you get a TF100 kit you could measure <20 which would help some to figure it out

would be interesting to see the source data for ±15 and ±10 to see if they apply over the whole range or if at the low end it is better or worse

ah ha found from JasonLion
The precision of the test, when done correctly, is around plus or minus 15 for levels up to 90 and plus or minus 30 for levels between 100 and 200. Novices often have problems reading the test correctly, and tend to get higher than actual readings.

so ± 15 applies to the low end

 

[MBG75]

Did you ever get the ammonia test?

 

[chem geek]

You can only realistically test for ammonia BEFORE you've added any chlorine or at least when the FC is showing 0. There can't be any ammonia in the water if there is measurable FC because chlorine combines with ammonia very quickly (less than a minute even with CYA in the water) to form monochloramine. The standard ammonia test kit actually uses Dichlor initially to convert ammonia to monochloramine and them measures monochloramine. So the ammonia test will measure the sum of ammonia and any existing monochloramine, but will usually report this in ammonia (ppm N) units that are a factor of 5 lower than chlorine (ppm Cl₂) units. The following example shows what would happen if you measured starting with 5 ppm ammonia (as ppm N), then added 10 ppm FC, measured again, then added another 50 ppm FC.

Step .............. Ammonia (ppm N) . Free Chlorine (ppm Cl₂) . Combined Chlorine (ppm Cl₂) . Test Kit Ammonia (ppm N)
Start ....................... 5 ............................ 0 .......................................... 0 .................................. 5
Add 10 ppm FC ......... 3 ............................ 0 ........................................ 10 .................................. 5
Add 15 ppm FC more . 0 ............................ 0 ........................................ 25 .................................. 5
Add 10 ppm FC more . 0 .......................... 10 .......................................... 0 .................................. 0

In practice, you can get more of a mix since chlorine does start to oxidize the monochloramine as it builds up, but you can see that the test kit measures the sum of ammonia and monochloramine (real ammonia + CC/5).

Looking for ammonia when there is an almost immediate consumption of FC and where CC is seen makes sense, especially when there has been a drop in CYA such as over the winter or whenever a pool got to 0 ppm FC. Looking for ammonia when FC is holding at least for several minutes doesn't make sense.

 

[wayner]

I never bothered with the ammonia test.

An update - I added 1.8kg of GLB CYA on 7/17. I tested on 7/24 and got a measurement of about 50 for CYA. On 7/25 I added another 900g of CYA and I tested this morning and got a reading of around 57. Once this last batch fully dissolved I should be in the 60s so I guess I am set for now. Now to get my SWCG working again!

As someone mentioned in another thread - surely there has to be a better way to measure concentrations than the disappearing black dot test. That just doesn't seem accurate to me as two different people could give very different results - even with myself I am not sure when to see that the black dot has completely been obscured so I add a bit more. Personally I would guess that the error would be easily +/- 10 at the 50 level and a higher level at higher concentrations.

 

[wayner]

Re: connection between air in the return and CYA consumption

I am the OP regarding air bubbles from the solar panels. I have been adding CYA but my last addition was a week ago so my CYA should be stabilized around 60. I will keep an eye and see if it decreases quickly over time. But I hope to have my air bubble situation fixed soon as well.

 

[wayner]

Re: connection between air in the return and CYA consumption

Yes, whereas a pool may lose 2-3 ppm CYA per month

How would you even tell if you had a 2-3 ppm CYA loss? It seems to me that the margin of error with the Taylor CYA disappearing black dot test is about 5 pm, likely more at higher concentrations. Or are there better tests that you have access to?

 

[chem geek]

Re: connection between air in the return and CYA consumption

I measure over 6 months and divide by 6. I've seen between 10 and 20 ppm CYA loss in that time so it's just a rough estimate.

 

[wayner]

Re: connection between air in the return and CYA consumption

I measure over 6 months and divide by 6. I've seen between 10 and 20 ppm CYA loss in that time so it's just a rough estimate.

Ok good, that makes more sense. How frequently do you do the CYA test? The Taylor K-2006 kit offers only enough reagent due to about 7 tests. That's not even enough for a season up here in the northern climes assuming a few tests early in the year to get you up to the right level and then a test every couple of weeks to make sure everything is still good.

 

[chem geek]

I hardly ever test the CYA -- usually only once or twice a season. I pretty much always test it after the winter rains have stopped since I use those to dilute the pool water. I then add CYA to get it up to around 40 ppm (I have a mostly opaque pool cover so don't need much, but I use 40 since I only add chlorine twice a week so the swing in FC has less of an effect on the active chlorine level at higher CYA -- I used to use 30 ppm CYA but 40 ppm CYA is better for a 3 to 6 ppm FC range).

As noted in the Pool School article Test Kits Compared, the Taylor K-2006 has reagent volume for only around 8 CYA tests while the TFTestkits TF-100 can do around 16 tests. The TF-100 was designed with a more intelligent balance of reagents that one uses the most.

When I was testing the CYA level to see how quickly it dropped, I tested for a couple of months and saw it hardly moving so then waited over a total of over 6 months. Because of the mostly opaque safety cover, I have very little evaporation and refill (not that this changes CYA, but it also keeps CH and other parameters more stable) and have very little splash-out and carry-out though there is some from the pool being used by my wife almost every day. So pretty much any CYA loss is due to it getting oxidized by chlorine. Also, CYA getting oxidized by chlorine shows up as part of daily chlorine demand because for every 1 ppm CYA that is oxidized by chlorine, it uses up 2.5 ppm FC. So 2-3 ppm CYA loss per month is 0.17 to 0.25 ppm FC per day. This will be very temperature dependent and in my pool is at around 88ºF average temperature.

 

[wayner]

Stop teasing me about hte TF-100 kits since they can't/won't ship to Canada! I will get one shipped to my SIL in Dallas and have her ship it or bring it to me.