Newbie question about automatic chlorinators

[Htown Tiger]

Hello all. Been lurking for a while and reading a lot of good info that has helped me as a new pool owner.

I had a general question about chlorine pucks and automatic chlorinators (and yes, I have read plenty on how these are not preferred, can raise CYA, etc. However, that is not the intent of this question):

If I have my setting on a specific dial that will dissolve 1 puck per week, if I add 2 pucks the next time, will it:
(a) simply last 2 weeks?
(b) still last 1 week, but the "concentration" of chlorine will be 2x as strong?
(c) somewhere in-between (i.e. might last longer than 1 week but maybe not a full 2, concentration will be stronger than 1 puck but maybe not exactly 2x)?

Apologies for such a newbie question, still trying to understand and "get to know" my pool and system. I do supplement with liquid chlorine, for what its worth. But for now just trying to understand how the automatic chlorinator system works and how adding more pucks will impact my pool. Thanks in advance!

 

[ajw22]

Depends...

• upon the tablets as tablets from different manufactures dissolve at different rates
• upon the water flow through your system and chlorinator
• upon the specific chorinator you have

You have to experiment and observe how thinsg work in your pool system.

 

[Htown Tiger]

So I had a follow up to this question, if anyone is able to help answer:

I put 2 pucks in the chlorinator, at a setting of 3 (out of 5), and it lasted me 8 days (approximately 104 running pump hours). Is there any way to back into how much chlorine and CYA these 2 pucks added to my pool on average each day?

 

[mknauss]

Sure. Use Effects of Adding Chemicals in PoolMath

Each 8 oz trichlor puck will add 6.9 ppm FC, 4.2 ppm CYA, and 5.6 ppm Salt to your pool.

So 2 of them, over 8 days, added 1.725 ppm FC per day and 1.05 ppm CYA per day.

It is likely your pool needs closer to 3 or 4 ppm FC per day to remain clean and sanitary. So be ware of that.

 

[Htown Tiger]

Awesome, thank you!

 

[Toxophilite]

That's the inherent issue with pucks, it's always growing exponential. Added CYA begets need for more FC, more FC breeds a new and higher CYA level, which begets a new higher FC level........

 

[Htown Tiger]

I'm definitely realizing that. My CYA is already at 60. If I'm doing the math correctly (now using PoolMath), along with 2 pucks, I need about 60oz of LC per day to maintain proper levels. And then that will continue to increase over time as the CYA ultimately increases. Eesh.

 

[ajw22]

That's the inherent issue with pucks, it's always growing exponential. Added CYA begets need for more FC, more FC breeds a new and higher CYA level, which begets a new higher FC level........

No, it really does not work that way.

With higher CYA levels your target FC level will rise. But that is a one time top off to the new target.

Your FC daily consumption of 3-4 ppm will not change as the CYA level rises.

At CYA 30 your high end FC target is 6 and minimum is 2. Your daily FC loss is 3-4 ppm and your FC varies between 2 and 6.

At CYA 80 your high end FC target is 11 and minimum is 6. Your daily FC loss is 3-4 ppm and your FC varies between 7 and 11.

Your daily liquid chlorine addition is 3-4 ppm regardless of CYA level.

As your CYA increases you do need to do some one time liquid chlorine additions to increase your target FC.

 

[Toxophilite]

No, it really does not work that way.

With higher CYA levels your target FC level will rise. But that is a one time top off to the new target.

Your FC daily consumption of 3-4 ppm will not change as the CYA level rises.

At CYA 30 your high end FC target is 6 and minimum is 2. Your daily FC loss is 3-4 ppm and your FC varies between 2 and 6.

At CYA 80 your high end FC target is 11 and minimum is 6. Your daily FC loss is 3-4 ppm and your FC varies between 7 and 11.

Your daily liquid chlorine addition is 3-4 ppm regardless of CYA level.

As your CYA increases you do need to do some one time liquid chlorine additions to increase your target FC.

What I mean is along the lines that to do "industry standards" of 1 - 3 ppm, if using tabs, I put 2 tabs in the chlorinator, which last about 1 week, and at best would keep my pool at 3pmm, tops. Done that at first till I found this place and learned you can't stay 1-3 ppm and be blind to CYA levels and just superchlorinate once per week to make up the difference.

As the CYA builds, and going by the CYA/FC chart here, my FC level then needs to be maintained much higher. I did that by adding more tabs, which worked and brought me up to 5-6pmm. Still, lasted about 1-week in the chlorinator. So, I went from adding 2 tabs/week worth of CYA to 4 tabs/week. My thoughts are that one cannot use tabs without substantial CYA degredation and follow the TFP method. Incompatible.

 

[ajw22]

I agree that "industry standards" for Trichlor use and TFP methods are different and incompatible.