Does everyone need Stabilizer?

[athan01]

I finally got my hands on a proper test kit (Taylor K-2006) and I was able to take proper measurements of my pool:

............FC (ppm).....CC (ppm)..........pH..............TA..............CH..............CyA
Test 1........ 6 .............. 3..............7.4.............150.............425.............~15
Test 2........ 6............... 0..............7.4.............140.............375..............~0

My tests were conducted with a few days difference. I keep my pool covered at all times, except when we use it and lately this has been infrequent (2-4 times a week or so). Even though I live in a very sunny country, keeping the pool covered for most of the day seems to be helping in maintaining my pool FC levels.

My CyA levels are very low, but my FC seems to be within limits. My SWG works well so believe I have reached a balance where FC is being generated and used in an even way (at least with the current use/covering of the pool)

So the question is: Do I need to add CyA, if i dont have an issue with the sun dissolving my FC?

Thanks
Andreas

 

[chem geek]

Yes, you absolutely need CYA because it isn't there just to protect chlorine degradation from sunlight but also to significantly moderate chlorine's strength. If you did not have CYA in the water and had just 2 ppm FC, this would be an active chlorine (hypochlorous acid) level that is nearly 40 times higher than the FC/CYA levels recommended for SWG pools in the Chlorine / CYA Chart. Now since you keep your pool covered most of the time, you could get away with a lower CYA level of say 30 ppm or so and have an FC target of only 2 ppm. Or you could have your CYA at 50 ppm and keep your FC at 3 ppm. Either way, the chlorine will be far less noticeable compared to not having any CYA in the pool where your swimsuits, skin and hair will get oxidized much, much faster and your pool cover will degrade that much faster as well. Without CYA, you'll also have faster creation of disinfection by-products and faster corrosion of equipment.

With your first test if you truly had 3 ppm CC then that is extremely high. I suspect something was wrong with that measurement.

 

[athan01]

Chem Geek,
Thank you very much for the (always) comprehensive and idiot-proof explanation. This is definitely useful data.
Let me complicate things a bit more: In my ignorance, I thought it would not be relevant to say that I seem to have an algae problem (mustard algae) which I somehow cannot get rid of. I couldn't SLAM the pool before i got the test kit, and since i got it I did not have the time to deal with this issue seriously -which I must do at some point soon-. The algae keeps reappearing after a couple of days on the bottom of the pool, resembling sand. If I decide to slam, i guess is better if I do it before I add Cyanuric acid, as this will make my SLAMing process easier -add less chlorine.

Am I on the right track?

 

[duraleigh]

Am I on the right track?

Dose enough CYA to get to 20-30 ppm before you SLAM. If you don't you will lose excessive chlorine to the sun.

 

[chem geek]

And you'll want to keep your pool uncovered during the SLAM process so you can outgas volatile chemicals, create hydroxyl radicals from the breakdown of chlorine by the UV in sunlight, and avoid exposing your cover to a high chlorine level for too long. You can have your cover over the pool perhaps for one or two days during the SLAM process so that it gets exposed to high chlorine at least part of the time to kill off any algae on the cover, but you don't want it on the entire time.

 

[bobodaclown]

Indoor pools do not need stabilizer.

 

[jblizzle]

Indoor pools do not need stabilizer.

We recommend CYA for indoor pools as well (as low as you can measure), not for the sun protection but for the chlorine buffering as chem geek mentioned a few posts up.

 

[chem geek]

Not only indoor pools, but spas as well. If you don't have any CYA in the water, then the chlorine is far too strong and it is completely impractical to try and maintain only a 0.05 to 0.1 ppm FC level which is the equivalent in active chlorine (oxidation power, disinfection rate, rate of creation of disinfection by-products, corrosion rate, etc.) to the levels found in the Chlorine / CYA Chart.

This is one reason why German DIN 19643 targets a low 0.3 to 0.6 ppm FC with no ozonator or 0.2 to 0.5 ppm with an ozonator because they have no CYA in the pool and want to minimize disinfection by-products and other negative effects from chlorine. There is simply no need to have higher chlorine levels since there are so many negative side effects to doing so. If one has a high bather-load pool or spa, as with commercial/public pools and spas, then supplemental oxidation may be used or one can use the German DIN 19643 approach of coagulation/filtration but requires slower flow through filters than found in most newer U.S. commercial/public pools.