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

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.

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

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

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?

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

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.

He was just using my spreadsheet where you enter in the pH, FC, CYA and other parameters and I calculate the HOCl concentration. He isn't measuring it directly. He just wants to know how the spreadsheet calculated HOCl concentration relates to the tables of FC and CYA that Ben and I did (I based mine roughly on Ben's, but made it consistent in HOCl concentration for each column).

Yes what chem geek described in the last post was exactly what I was trying to acheive.

The reason being that even though it is recommended that the Pool Pilot Total Digital SC-60 be mainted at 3 ppm measured chlorine I have found that to be too low as small spots of yellow algae start to form.

If I up the ORP to 700 it maintains around 5.5 FC at a pH of 7.4 and Alk at 70 (to reduce acid usage), calcium is about 580, borax 50, and cYA 35, salt 3000. This gives a calculated HOCL of about 0.075. 10,000 gals and pump runs 3.5 hours per day, from noon to 3:30 pm at 55 GPH (too reduce energy cost) as KWH is $0.27 in Hawaii and going up steadily.

This gives a algae free pool it might be that being at a lower altitude algae develops faster as the UV index is stronger.

It seems that having a bigger unit such as the SC-60 allows for stronger chlorine production and thereby allows lower run times, in Hawaii that is. It might be that different parts of the country can get away with less powerful units. I would be interested in any comments.

So far I have been very happy with the Pool Pilot Total Digital performance 10 out of 10, manual is not that clear or well written but adequate with calls to tech support 5 out 10, tech support is weak at level one they seem to be robotically answering questions and quickly become frustrated if one gets at all technical. At higher levels it gets better and if you drive them crazy enough you will finally reach the top level support which is excellent albeit that it can take you a frustrating 30 minutes of back and forward "that is not what I am saying and I need to know", 3 out of 10 at lower levels and 9 out of 10 at the top level ( one mark off for sounding a bit irritated that they had to answer the call).

Your experience lends further support to the theory that SWG pools can have a lower FC target because free-floating green algae gets super-chlorinated in the SWG cell. Yellow/mustard algae tends to settle and not free-float so won't get circulated as readily. So that would make the manual and SWG chlorine levels similar for that algae, namely an FC that is 15% of the CYA level.

For most SWG pools it is better to use a higher CYA level of 60-80 ppm since that will have the chlorine last longer (even at higher FC levels) and let you turn down your SWG output (since less absolute FC loss per day) which helps reduce the rate of pH rise. However, in your situation, that would require (in theory) an FC of 9-12 ppm to keep the mustard/yellow algae from growing.

This is one of those rare times where one of two things can be done. One is to super-shock the pool at 60% of the CYA level so in your case probably 25 ppm FC to be conservative and hold it there for several days and put everything and anything into the pool that might be harboring the algae, such as poles, etc. Even remove the lights from their niche to expose chlorine behind them. If you completely kill off the mustard/yellow algae, then it may not come back even at more normal FC levels.

The other option is to have your phosphate level checked and use a phosphate remover if its high (or even if its not, in this case). This is rarely suggested but it is another option to allow you to get to a lower sustained FC level. It's up to you what to do.

Richard

chem geek,

Thank you for your informative reply.

My question is (I am a little confused) if I just leave it the way it is as there is no algae visibly present and the unit is running at the mid-power setting of 2, which was recommended by the senior tech at Pool Pilot, would that not be the solution? Only issue is it does have to run nearly the full three and half hours to reach 700 ORP.

As you stated raising the cYA seems to me that I would need too much chlorine, which would require running the pool pump for a long period.

But the number I gave 5.5 FC appears to be ok from a health and swimming point of view, or is that not correct?.

I'm not sure where the yellow stuff comes from but where we live at a 1000 ft the trade winds roll over the mountain daily at about 16 mph to 26 mph on average blowing fine stuff (particles) constantly into the pool. So while we may cure it temporarily in all probabilty it will return just as fast. Therefore my feeling is to leave it as is, or do you think this is not wise? I will certainly give the phosphate suggestion a go and let you know if that has any effect I could become the pool stores only Diamond Card client if it does at least until I have to eat and stop buying phosphate remover.

The pool is pretty much 4 ft 6 in deep all the way round with steps into it, that is why I thought the UV may play a roll.

Finally what do you think is KWH use is of the SWG. I noticed in another thread on cost of chlorine nobody seemed to factor this in, or I could be mistaken.

As always thank you once again for all your great help. In this case I think I am between a rock and a hard stone.

It might be that the winds whip up a higher "Organic Load".

I found this article interesting; any thoughts?

http://www.water.siemens.com/SiteCol...20Chlorine.pdf

Many times people think they have yellow/mustard algae when they really have pollen. The main difference between the two is that the yellow/mustard algae will tend to stay on the shady side of the pool while the pollen will settle wherever circulation takes it and usually right on the bottom. Yes, pollen will create an extra organic load and therefore a chlorine demand. A skimmer sock is often the best way to remove the pollen as it tends to stay on the surface for a while so can get into the skimmer before it gets water logged and drops.

If you are able to get a sample of these yellow spots (carefully taking a turkey baster or something like that to suck some up), then if you look under a microscope you can tell the difference more readily. Pollen is round or spiky and solid-looking. Algae is more translucent and usually oblong.

You may be correct that you have pollen instead of yellow/mustard algae. That is usually the case. However, higher chlorine levels won't keep away pollen, but it will tend to break it down faster.

Richard

chem geek,

You are correct it is pollen, so now I keep the cover on and that seems to reduce the problem; taking it off for 2 hours a day to vent the pool.

Thank you for your help.