Aug 27, 2020
I am new here, and have my first swimming pool. I did read the 'Pool school' information, here and looked at many other sites.
I live in Thailand and since 6 weeks I have a new outdoor Fibre Glass pool with integrated spa built.
In total it contains approx. 50,000 litres water. The pool is filled with ground water. I have a SWG system with sandfilter.

Unfortunately my own ‘test tools’ are very limited:
- PH/CL testkit with two tubes where Phenol and Orthotolidne drops must be added (especially the Chlorine level is difficult to read, just guessing).
- a digital PH pen reader (quite accurate)
- test stripsTCl, FCl, PH, TA, TH, CYA (TCl out of range,other readings also not very reliable, I think)

The PH level in the water is always high and I have to add approx. 1,3 liter of HCL weekly.
Then I read on the TFP website about the problem of high concentrations of CYA I started to measure CYA with test strips. The CYA I measured is 150ppm. I was already planning to replace 73% of the the pool water (according PoolMath), but 'just to make sure' I went to have the water tested at a poolshop. There the CYA appeared to be only 11 ppm (tested with a La MotteColorQ PRO7)
As this is quite a big difference I decided to have ‘a second opinion’ and went right away to another pool shop to have the same sample water tested again. At this shop they measured for CYA 6 ppm only. Also other measurements were not in line with first shop. (There they use a La Motte Water Link Spin Lab).

Of course the shops don’t say whether they calibrate the equipment, and whether they use the correct reagents and doing the measurements exact according the instructions. At the other hand they are doing a lot of testing, so it cannot be that worse??

I am investigating possibilities to get my own ‘real’ testkit here in Thailand but it is difficult to get a Taylor or LaMotte test set (‘Restricted items’, import duty and VAT).

My questions:
What is the best to do now?
Which test is true? (the more different figures the more confusion)
Is it possible that the CYA is as low as the shops measured?
As I understand will the CYA always remain in the water. Taking in consideration that since the start up approx. 22 liters of HCL is added, are the low figures of the shops are possible then???

Any suggestions?
Thank you in advance,

Test results:
Idealshop 1test stripshop 1shop 2test striptest strip
Free ChlorineFC4 ppm0,820,5-11,252,611,001,00
Total ChlorineTC0,82??1,252,61????
Combined ChlorineCC0
Cyanuric AcidCYA70-8013150116150150
SaltTDS4000-5000 ppm317039004396
Calcium HardnessCH350-5502550385350100
PhosphatePhos0 ppb100100100
CopperCU0 ppm0,81
IronFE0 ppm0,26


Gold Supporter
LifeTime Supporter
TFP Guide
Jul 3, 2013
Fletcher, OK
Hans, I will start with this..

How did you put CYA in? Did you start out with 3 inch pucks that add CYA? Or did you add CYA manually with powder? We recommend CYA of 70 to 80 for Salt water pool so for you I would recommend 80 if your pool is in direct sun all day... I also run my chlorine high between 5 to 7 FC, I am also using SWG...

If you did not do pucks or solid CYA you do not have any CYA in it, and that would make sense why the shops say none or under 30 (hard to test under 30).. This is also why you are blowing through chlorine.... This is also why we say Strips are guess strips, you just never know what your going to get.... it will be worth it to pay whatever you need to to get a Taylor K-2006 C.. What are the shops testing with? and can you buy that test kit from them? I bet it is Taylor chemicals...


Aug 27, 2020
Thank you for your reply Cowboycasey,

'How did you put CYA in?' this is certainly a very good question.
I never put CYA pucks or CYA powder in.
The poolbuilders filled the pool and put in Chlorine powder and Muriatic acid and I only should add Salt, Soda Ash, HCL Acid and Swimtrine (in case of algae), thats it. Studying TFP learned me that there is more to it ;-)
I don't think they put the CYA in, but I try to find out.
That there is no/little CYA in the water would explain a lot!

The test strips are indeed not reliable and I am still busy trying to get a 'real' testset.
The shops were both using LaMotte test equipment ( ColorQ PRO7 and Water Link Spin Lab), but they don't sell this equipment.

Concerning these Acids:
- Is there any infuencing between the Cyanuric Acid (for stabilizing FC level) and the Muriatic Acid (for lowering PH)?
- For the Cyanuric Acid values when they become too high the water must be replaced. Is it also possible to get too high levels of Muriatic acid?

Thank you, I will keep you informed on progress


Gold Supporter
LifeTime Supporter
TFP Guide
Jul 3, 2013
Fletcher, OK
No issues between CYA (stabilizing, we like to say sunscreen for your chlorine) and MA and the only thing MA has influence on is PH and TA and it lowers both at the same time :)
never pour chemicals together... pour MA in front of a return by itself and put CYA in a sock in front of another return..

If you get 3 inch pucks it will raise your CYA and that is good.. Just stop using them once you get to 70 or 80 CYA.. you can use poolmath to find out how much each 3 inch puck will raise the CYA...
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Gold Supporter
Jun 28, 2017
Fresno, CA
Ask your pool builder what exactly was the "chlorine powder" that he added. Chlorine powder may include CYA (dichlor).
Keep searching for a proper test kit, other methods of testing fall short.