Total chlorine and cya

[KBKRH]

When I do the pool math, it recommends higher free chlorine.
I’ve always had free chlorine at 2-4 and higher cya and never have algae problems. Doesn’t seem to me that I should do the recommended higher free chlorine.
Here are my numbers.
Free chlorine 4. Combined chlorine 0. PH 7.7. Total Alk 65. Hardness 460. CYA 100. Water temp 66.

Need input why I should follow the pool math and increase the free chlorine to 10, if I’m not having algae problems.

 

[PoolStored]

Hypochlorous acid (HOCL) is what sanitizes a pool. The amount of HOCl in pool water is dependent on your FC and CYA levels.

The red line is generally accepted as the level of HOCL that will kill bacteria, the horizontal green line is the HOCl level that will kill algae.

When you run your pool at 4ppm FC, and 100 CYA, you are above the bacteria line, but below the algae line...thick blue lines.

The black lines are an FC of 11 and CYA of 100...you have enough HOCl to kill algae.

Increasing to your FC to the higher level will help you avoid algae.

How are you chlorinating? A CYA of 100 is high. I would stop adding any CYA containing chemicals (like pucks) to your pool and use liquid chlorine. CYA degrades over time and will come down. The only other alternative is to replace water to lower CYA.

Pool Water Chemistry

This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...

www.troublefreepool.com

 

[KBKRH]

Thank you very much for your explanation and chart. For the last while I’ve been using liquid chlorine and not pucks. I’ll continue using liquid to get the cya down. Swimming season is over in the Dallas, Tx area. What level of free chlorine should I not go below? Present water temp is 66.

 

[reggiehammond]

What are you adding to your pool? Only liquid chlorine? Acid? Shock? Clarifier?

 

[Newdude]

Also, algae is microscopic and by the time you can see it, it's already a runaway train. (It grows exponentially). People can keep a bloom just on the clear side for an extended time, believing that there is no algae.

Algae, while unsightly is harmless. But it's the canary in the coal mine and if it can grow, so can the bacteria and virus and such that are the real concern. You need to be clear, *and* sanitary, not just clear.

90+ CYA is sketchy to read at best, you need to do a diluted test and double the result. Mix up a batch of 50/50 pool and tap water. Procede with the rest of the test and double it. It may be much higher than 100 and you'd need even more chlorine to remain sanitary. All levels on this chart are considered equal for sanitizing. Keep the proportions going for 100+ and you'll see how quickly it gets out of hand.