Lowering CYA/Maintaining correct levels

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L

longbody

0
In The Industry
Nov 22, 2015
5
Santa Cruz, CA
I bought a pool route in Santa Cruz with 30 pools. Practically all of them have CYA of 150-200 ppm.

Due to the water shortage, it's nearly impossible to get folks to drain 1/3 - 1/2 of their pool and refill. With the predicted high rainfall we're expecting, I was going to recommend that, when they expect a heavy rain, to drain 1-2" and let the rain refill it.

1st question: In some long ago chemistry class I seem to remember that draining before the rain would dilute the solution more than draining after the rain. If this is correct, does anyone have the formula that proves this?

Draining/refilling will take care of the problem but very slowly. I plan to use Bio Active enzymes to 'disassemble' the CYA molecule so the parts can off gas or be filtered out. This will have to wait until Spring since the enzyme won't work unless the temperature is >65.

2nd Question: I get mixed feedback from other pool pros - some say it works, others say no. Any 1st hand experience with this product?

Another step in lowering and maintaining the correct levels is to stop adding it. Most of the pools are using floating dispensers with dichlor tablets. The manufacturer tells me that they are 50% CYA so finding a different way to chlorinate is necessary.

  • Calcium Hypochlorite has no CYA but increases Calcium Hardness
  • Lithium Hypochlorite is at least twice the price
  • Chlorine gas would work but I've decided not to do that
  • Sodium Hypochlorite seems to be the way to go

3rd Question: Since I treat these pools weekly, should Sodium Hypochlorite keep the FC level up for a week? I think that if I bring it to 5 ppm, it should stay above 2 ppm by the time I return the following week. Feedback?

4th Question: Right now I include Sodium Hypochlorite in my monthly service charge. If I replace the dichlor with Sodium Hypochlorite, I will have to charge for that instead of the tablets. My customers are going to want to know if there is going to be a difference in price. I have records of how much dichlor they have used over the last year. If the tablets are 50% chlorine, that means a 25# pail contains 12.5# of chlorine. Sodium Hypochlorite is 12.5% chlorine so a gallon contains 16 fluid ounces of chlorine. I know there's a conversion formula here but I'm not sure what it is - anyone? Bottom line - I need to tell my customers if the conversion is going to cost more, less or stay the same

Thanks,
David Boggs
Clearwater Pool and Spa
Santa Cruz, CA
 
Hi Welcome to TFP!
Obviously you are aware of the CYA issue with using trichlor tablets as the primary source of chlorine. I can tell that by FAR, people who come to TFP come here looking for help because their pool service technicians and pool shops havre used / recommended trichlor tablets, and the CYA has gotten so high, that it becomes impractical to add enough chlorine to the pool so as to overcome that amount of buffering effect.

Below the pool school button is a search field and you can use to find serveral discussions here on TFP about BioActive. Several of our members have tried it and ultimately, the conclusion is that it "may" lower CYA a little - sometimes, but it doesnt stand up to the hype. We also had the bioactive rep involved in our discussions as well.
TFP doesnt recommend it because its hit and miss.

We agree that sodium hypochlorite is the way to go. I would like to note however, that most of our recommendations and pool care methodology is directed towards Pool Owners who wish to maintain their pools themselves.

Regarding your 3rd questoin. Your FC range seems to be based upon standard pool industry recommendations. I have to tell you that TFP doesn't agree the industry standard for FC because even though they know about it, they do not recognize the FC/CYA relationship. Proper FC to keep the pool sanitary and free of algae depends on the CYA level. I invite you to read this.
Certified Pool Operator (CPO) training -- What is not taught

And this one Pool Water Chemistry

your 4th question I cant help you with. Maybe someone else will chime in.

Good luck with your pool route!
 
On my. Drain before, although I can't give you a formula. It's just common sense.

You need a good testkit with lots of reagents. Do you have one?

Also, to be a good service, you need to attend to these pools more than weekly, especially until you get things under control.

Bio-active has not had great reviews.

You need to read up on our methods in pool school and focus your attention on the FC/CYA relationship.
 
Draining before is more effective because you initially remove high CYA water. If you don't drain before and the water level rises but does not overflow, then subsequent evaporation will return things to exactly as they were before. Even if there is rain overflow, you will remove very little CYA if the rain doesn't mix with the rest of the pool water (i.e. if the rain sat mostly on top of the pool water and overflows, it won't remove much CYA) and even if it did mix that is more like continuous dilution which is less efficient. Don't forget that if you do a drain ahead of time you need to turn off the auto-fill or else you'll use that water instead of rain water.

See Certified Pool Operator (CPO) training -- What is not taught for info on what each type of chlorine adds to the water.

There are some pool services that use chlorinating liquid or bleach weekly, but to do that you have to have a higher CYA level to prevent chlorine loss from sunlight -- usually close to 100 ppm in sunnier climates -- and you need to raise the FC higher to around 14 ppm to end up at 4 ppm a week later. That gets below the minimum FC/CYA ratio, but the rise to 14 kills off anything that gets started at the end of the week. That's one approach, but most pool services use Trichlor pucks because that's the only slow-dissolving source of chlorine that can last a week. To handle the CYA rise they either dilute the water or use supplemental products (algaecide or phosphate remover) to prevent algae growth. Some pool services try and split the difference by using less Trichlor and raising the FC with chlorinating liquid weekly.
 
Marian,

Thanks. Yes, I use the Taylor K-2005 and have a K-2006 as well. I also use Taylor's TDS, Copper and Iron Test kits.

I used a automatic chemical control/feeder one one of the commercial pools I treated and it integrated ORP which is the best measure of sanitation. I've been thinking about getting a portable one.
 
Thanks, Dave.

Actually, when I renewed my CPO, Taylor taught the course and they taught the CYA relationship as regards TA. They say to divide CYA by 3 and subtract that number from TA to arrive at Total Carbonate Alkalinity.

They didn't mention FC/CYA relationship. Can you point me toward where the information that will tell me how the 7.5% number was derived?

Also, question 3 was for after I get the CYA down to 30-50 ppm. Using the 7.5% rule, FC would be 3.25 ppm (at 50 ppm CYA). So I was thinking if I left it at 5 (or even 7) ppm, it would still be reasonably safe until I got back the following week. Does this sound right?
 
Chem Geek,

Thanks as always.

I found your pricing in a different area (posted below) which is just what I need.

If I can make the numbers add up for the customer, I'm going to try to offer to set up their pools like the commercial pools I've handled - peristaltic feeder with a 15 gallon carboy so I can use liquid.

I had one question, though. The chlorine I buy is 12.5%. How did you arrive at 10.8% chlorine?

Thanks


...cost per available chlorine ...:

Trichlor Tabs/Pucks ......... $2.20 / 0.915 = $2.40 but $3.83 when accounting for Washing Soda to adjust pH
Dichlor .......................... $2.60 / 0.554 = $4.70 but $5.73 when accounting for Washing Soda to adjust pH
73% Cal-Hypo ................ $2.40 / 0.724 = $3.31
Lithium Hypochlorite ....... $6.00 / 0.352 = $17.05
12.5% Chlorinating Liquid . $0.336 / 0.108 = $3.11
6% Bleach ..................... $0.15 / 0.057 = $2.63
 
longbody said:
I used a automatic chemical control/feeder one one of the commercial pools I treated and it integrated ORP which is the best measure of sanitation. I've been thinking about getting a portable one.
Click to expand...

If you spend enough time on this site reading the information here, you will come to realize that ORP is, in fact, a very poor way to control residential pool sanitation. The best measure of sanitation is the active chlorine (hypochlorous acid) level and that is not exclusively related to ORP. ORP is affected by many variables not least of which include sunlight exposure, pH, alaklinity, dissolved oxygen, and any chemical species that contributes to the oxidation-reduction potential of water. CYA reduces and moderates the level of hypochlorous acid in pool water and therefore lowers its effect on ORP voltage. CYA also fouls the membranes in a lot of ORP sensors rendering them useless. While it is true that commercial pools use ORP sensors to control chemical dosing, no commercial pool is allowed by regulatory authorities to use ORP as a reporting requirement for sanitation, they must report FC and CC levels as measured by a chlorine test kit.

As a new member, I would urge you to go to the search bar and enter terms like "ORP" and "chem geek" and you will find volumes written on the short comings of ORP control. Save yourself the money on a portable ORP probe and stick to Taylor titration testing.


longbody said:
They didn't mention FC/CYA relationship. Can you point me toward where the information that will tell me how the 7.5% number was derived?
Click to expand...

This post by chem geek is the definitive post on pool water chemistry. Read it....several times....
 
longbody said:
I had one question, though. The chlorine I buy is 12.5%. How did you arrive at 10.8% chlorine?
Click to expand...

Those prices are pretty old, but their relative relationship shouldn't be too far off. The 12.5% is Trade % which is the VOLUME % of available chlorine. For the comparisons I used the normal definition for % Available Chlorine which is a WEIGHT %. The difference is due to the 1.16 density of 12.5% chlorinating liquid (12.5/1.16 = 10.8).

As for the 7.5% rule for non-SWCG pools, that was not determined directly from chemistry, but from observations Ben Powell made years ago with regard to when algae growth started to occur. He had a rough range table, not a percentage, but the chemistry shows that the active chlorine level is proportional to the FC/CYA ratio so I normalized his ranges to a table following this percentage rule and came up with 7.5%. Since that time we've validated this in many thousands of pools over the years and also determined that SWCG pools could use a 5% target instead. So while the fundamental chemistry says that the ratio is the determining factor for preventing algae growth at any (even highest) level of algae nutrients, the actual percentage itself was determined through observation.

Note that pools that use supplemental algaecides or phosphate removers or that are naturally lower in algae nutrients (phosphates, nitrates) can target a lower percentage (FC/CYA ratio), but we have not characterized this specifically in order to keep the rule simple. Nevertheless, one can do this approach either to save more money or as insurance so for weekly pool services it may make more sense.
 

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Well, I converted prices to price per weight and then compared by chlorine content by weight. I could have done the same thing by volume instead but most products are sold by weight. The exception is the chlorinating liquid or bleach which are sold by volume (i.e. $/gallon). Ultimately, you want to convert any way you like but end up comparing actual dollars per chlorine amount (i.e. resulting FC).
 
@JoyfulNoise.
I thought ORP was great indicator of the pools ability to oxidise compounds.
Controller Concepts: ORP and Oxidation Part I | PPOA

Quote from above link.
Extremes showed up in pH from 5.7 through 8.3, combined chlorine from 1.4 to 34 ppm, free chlorine from 0 to 30 ppm, cyanuric acid (what’s it doing in a spa??) from 0 to 1,300 ppm, plate counts from 0 through 15,000, and even Pseudomonas up to 12,400! The only correlation that stood up throughout the study was the relationship between ORP and the presence of pathogens
 
Just as an idea, you may want to also consider trying to sell them all on the idea of purchasing an SWG. Besides it being easier on you with only visiting weekly and better able to maintain the TFP way without being there daily you could sell it based on the water savings alone without CYA issues forcing expensive and/or banned refills.

LOL, the way CA likes to pass laws I'm surprised they haven't banned CYA containing chlorination methods themselves already to save the environment, water supply, and some toads.
 
TheEng said:
@JoyfulNoise.
I thought ORP was great indicator of the pools ability to oxidise compounds.
Controller Concepts: ORP and Oxidation Part I | PPOA

Quote from above link.
Extremes showed up in pH from 5.7 through 8.3, combined chlorine from 1.4 to 34 ppm, free chlorine from 0 to 30 ppm, cyanuric acid (what’s it doing in a spa??) from 0 to 1,300 ppm, plate counts from 0 through 15,000, and even Pseudomonas up to 12,400! The only correlation that stood up throughout the study was the relationship between ORP and the presence of pathogens
Click to expand...

Kent Williams and his "work" with PPOA has been discussed and debunked on TFP many times before. Simply look up "Cyanurics - Benefactor or Bomb?" in the search box and you'll get many threads discussing this stuff. Nice that Kent doesn't disclose his previous work with ORP Manufacturer Stranco in all of his work...

The bottom line is ORP does not work well in residential, outdoor pool unless you keep tight control over all your water parameters AND you use very low (read - ineffective) levels of CYA AND you constantly maintain & clean the ORP probes on a weekly basis. Even then, you will get an ORP system that over-burdens your chlorine production system because the low CYA levels will cause a huge FC demand from UV photolysis. There is simply no way to make these systems work in a trouble-free, low maintenance manner and, it is the opinion of many, that they are a waste of time and money when one can simply automate chlorine production using an SWG or a liquid chlorine pump and get fantastically stable results.

Commercial pools and spas are a totally different subject matter entirely and almost none of them use CYA so ORP control is a lot easier to correlate to FC.

But answer me this - if ORP is so fantastic, then why does no regulatory health department charged with overseeing public pools allow it to be used as a reporting requirement? They all want actual FC/CC and pH data logged (sometimes hourly) using standard titration methods. Not a ringing endorsement by any means...


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006
 
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