Of the CYA range 30-50 (or even 30-80), what's the sweet spot?

robininni

Gold Supporter
Dec 6, 2016
18
Stephenville
So as I understand it, as CYA increases, it protects FC better from destruction by sunlight. As CYA increases, you need more FC for the same level of sanitizing effect. You will lose some of this FC to sunlight every day and have to add chlorine to maintain these levels. The 'goal' according to Pool Math is 30-80 ppm CYA, depending on whether you are going by the Traditional Pool or Trouble Free Pool criteria. But is there a best number? I am going with the TFP criteria so it's the 30-50 ppm range for me.

I'm sitting at 41 ppm CYA and am trying to decide whether to hold it at that level of get it to 50 ppm. According to the handy chart here on TFP, at 40 ppm CYA, you need a minimum of 3 ppm FC and more favorably 5-7 ppm. At 50 ppm CYA, you need a minimum of 4 ppm FC and more favorable 6-8 ppm. So.... is one better than the other?

Since more CYA protects the chlorine better but yet the more CYA you have, the higher the FC level you need to maintain, at what level of CYA have you reached the optimum of free chlorine protection from sunlight versus higher required free chlorine? At higher CYA levels I assume you lose less FC to sunlight each day, but at what point does this reduction in FC loss justify the increase in required FC level that must be maintained? Assuming you have the free chlorine at the proper level for a given amount of CYA in you pool, at what level of CYA are you having to add the least amount of chlorine to the pool on a per week basis to maintain the desired FC level?
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,874
Tucson, AZ
There is no real "sweet-spot"...juts find a value that works best for you. Your goal is not lose more than 2-4ppm per day and to dose at a frequency that is easiest for you to maintain. Some people have no problem dosing every day; others would rather stretch out the dosing by a few days. It all depends on what you need and want. I keep my CYA up at 90ppm because of the intense sun and heat here and I have an SWG. In a manually chlorinated pool, most people find that something around 50ppm is easy to manage if you get a lot of sun. You just have to find a value that works best for you.
 

OTPirate

Admin
In The Industry
Oct 2, 2013
1,346
Creedmoor, NC
The K-2006 comparator reads in increments of 10, so I'm assuming you are just a tiny bit above the 40 ppm mark. I wouldn't sweat a difference between 40 and 50 ppm CYA.
 

robininni

Gold Supporter
Dec 6, 2016
18
Stephenville
The K-2006 comparator reads in increments of 10, so I'm assuming you are just a tiny bit above the 40 ppm mark. I wouldn't sweat a difference between 40 and 50 ppm CYA.
Correct, I inferred a level of 41 ppm of CYA due to the level of the water in the vial in relation to the 40 and 50 ppm marks after completing the test.

I was going to get my CYA up to 50 ppm and so I added 8 pucks of trichlor to my inline chlorinator today which, when all dissolved, would get me very close to that but I've decide to hold at my 41 ppm and so turned off the chlorinator. I will be adding sodium hypochlorite only for chlorine now to maintain the CYA level. It seems it is unknown whether there is a benefit going from my current CYA level of 41 ppm to 50 ppm as far as the increased chlorine protection making it so that I would be adding less chlorine a week to maintain proper levels of FC. Since this is unknown, I'd rather have less chlorine in the pool to get the job done and, as a plus, my test strips I use between serious testing work well with the minimum and target values of FC for CYA levels at 40 ppm since they have 3 ppm and 5 ppm FC marks.
 
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