Target numbers for an indoor pool?

[Isaac-1]

After dealing with a broken return pipe and having to drain and replace about 50% of the pool water it is time for me to get the 20x40 indoor vinyl pool at my mother's house balanced for the spring this year. I have invested in a new TF100 test kit and now wanted to get some advice on numbers to shoot for? I plan to use chlorine bleach to get initial levels right without causing CYA to get to high. While this is not starting from a clean slate, it is probably as close to a clean slate as I am going to get.

thanks Ike

 

[PoolGuyNJ]

Skip the CYA unless the enclosure is glass. That means no tabs or di-chlor.

Shoot for:
Alk level of 80-100
pH No Heater 7.2-7.4 - With heater 7.4 -7.6
Free Chlorine 2-3 ppm
Total Chlorine = free chlorine

CYA protects chlorine from UV energized dissipation. If the sun isn't hitting the pool surface, the CYA would just lock up the free chlorine needlessly.

Scott

 

[frustratedpoolmom]

We actually recommend a small amount of CYA in an indoor pool, about 20 ppm

I'd shoot for 4 ppm FC with 20 ppm CYA, but not a lower FC/CYA than 3 ppm FC with 30 ppm CYA. You want a higher active chlorine level in an indoor pool since there is no sunlight to help breakdown or accelerate the oxidation of bather waste. On the other hand, if you have no CYA at all, as is usually recommended by the pool industry for indoor pools, then the chlorine would be too strong (in Europe using the German DIN 19643 standard they don't use CYA, but have the FC be 0.3 to 0.6 ppm and use activated carbon filters to remove all chlorine and chloramines and re-add chlorine with each filtration pass). It is not practical to have 0.2 ppm FC with no CYA which would be equivalent to the 4 ppm FC with 20 ppm CYA I recommend.

Other than that, the other water parameters can be set according to the normal recommendations.

Richard

We recommend CYA levels around 20 for indoor pools. Adding a little CYA to the water prevents high FC levels from damaging hair and swim suits, and reduces the production of some of the more annoying forms of CC.

 

[Isaac-1]

Thanks, I will let you know what the initial numbers look like this weekend.

Ike

 

[chem geek]

Skip the CYA unless the enclosure is glass. ...
...
Free Chlorine 2-3 ppm
...
CYA protects chlorine from UV energized dissipation. If the sun isn't hitting the pool surface, the CYA would just lock up the free chlorine needlessly.

As FPM noted, if you don't use any CYA at all and use an FC level of 2-3 ppm as you suggest, then compared to the 4 ppm FC with 20 ppm CYA that we recommend you've got 10-20 times as much active chlorine (hypochlorous acid) in the pool which will oxidize swimsuits, skin and hair up to 10-20 times faster and also likely produce about 10-20 times as much irritating and volatile nitrogen trichloride. The significant reduction in active chlorine when CYA is present is not a bad thing unless overdone. Essentially, pools with no CYA are over-chlorinated unless they have very low FC levels which is what the German DIN 19643 standard tries to achieve (but such low FC levels could "run out" of chlorine under local bather load conditions).

The downside to the lower active chlorine level is that it takes longer to oxidize bather waste and when there is no UV in sunlight to help you it's possible to build up more CC, at least temporarily. Indoor pools are a challenge and often need supplemental oxidation (UV or ozone) unless the bather loads are very light and this is true even when no CYA is used.

 

[Isaac-1]

Well I am reporting back on initial numbers:

Chlorine 0
PH 6.9
CYA something less than 20 ppm (as low as the test goes, but it was getting cloudy)

I did initial treatment to try to get into the ballpark, and will retest in more detail tomorrow, I did not get as much done as I would like. I found a vacuum side leak, and spent more time than I wanted chasing it down.

 

[Isaac-1]

Back again, things are getting closer, I swam in it today, still a bit cool (solar heater panels need repair/replacement) should be ready for the big family gathering next weekend I hope.

FC/CC numbers from today, others from yesterday

FC 4 ppm
CC .5-1.0 ppm (shocking now)
pH 7.6
TA 110
CH 340
CYA less than 20 (lowest measurement on TF-100,I added 2.5 lbs of powered HTH stabilizer last weekend, looks closer than last week so added another pound yesterday)

Ike

 

[chem geek]

CYA takes up to a week to register and you don't want to get too high so be careful about adding too much. I'd stop adding it and wait to retest in a week.