What is the best HOCL (as ppm CL2) number to aim for

[smallpooldad]

What is the ideal "HOCL (as ppm CL2)" number to aim for and does it matter what the temperature is if one uses the "Pool Equations" spreadsheet? If one wants to control most, or all, forms of algae.

Also what, or is there, a minimum acceptable number?

Looking forward to any replies.

[chem geek]

You should ask questions regarding the PoolEquations spreadsheet in The China Shop (and this thread should be moved there) as it is not for general users.

The correspondence between the various columns in Ben's Best Guess CYA chart and in my chart (at TFP) compared to HOCl concentration (and approximate FC as % of CYA) are as follows:

Minimum FC column corresponds to an HOCl of: 0.03 ppm (7.5%)
Target FC column corresponds to an HOCl of: 0.05 ppm (11.5%)
Maximum FC column corresponds to an HOCl of: 0.07 ppm (15%)
Yellow/Mustard Min FC column corresponds to an HOCl of: 0.07 ppm (15%)
Shock FC column corresponds to an HOCl of: 0.3 ppm (40%)
Yellow/Mustard Shock FC column corresponds to an HOCl of: 0.7 ppm (60%)

The correspondence with Ben's Shock FC column is only approximate -- his chart has a higher FC at lower CYA and a lower FC at higher CYA than based on HOCl concentration.

Richard

[smallpooldad]

chem geek,

My apologies I will go to China Shop if a question of this sort arises again and now request that this post be moved to the China Shop as I do not know how to facilitate this operation.

Your answer was clear and is very helpful with balancing the water especially to combat marine algaes found here in Hawaii.

Aloha

[Water_man]

I know that curiosity killed the cat, but I wonder, since the goal is to combat algae, why would you care about HOCL levels, if all the charts, the calculations, and the tests are based on FC?

[chem geek]

The easiest way to look at it is that the industry has never developed the appropriate chemical test to determine the true amount of disinfecting and oxidizing chlorine (that is, hypochlorous acid). The closest tests are expensive sensors with selective membranes that measure hypochlorous acid level and ORP sensors that are a rough proxy for it (though they vary by sensor manufacturer).

The Free Chlorine (FC) level is a simple chemical test, but it really just measures the total reserve of chlorine so will tell you whether you have enough total quantity to not run out if there is a certain rate of consumption. It does directly not tell you the rate of disinfection, algae kill, or oxidation.

Fortunately, the chemistry of chlorine, Cyanuric Acid, and their combinations is well understood (has been since at least 1974) so one can use the FC/CYA ratio (or FC percentage of CYA) as a reasonable estimate of the hypochlorous acid concentration. Though this ratio relationship varies somewhat with pH, it only varies by about 25% between a pH of 7.2 and 7.8.

Richard

[Water_man]

Granted the hypo-acid is the active species that actually does the job, but as you said, it's not simple to measure it. Do you think the original poster has a viable means to measure HA level? If not, what's the use? It won't have a significant practical implication and it can only cause confusion when using the "regular" FC charts, tests and calculations.
Just my 2 Cs.