Need a chemist - Cal Hypo

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S

Sark

0
Jul 2, 2017
15
California
Quick history of our operation:
I am NSPF certified and I run the bodies of water at a hotel/health club
1 33k gallon pool
1 75k gallon pool
3 spas 1300, 1300, and 1800 gallons.

For the past 10 years we have been using cal hypo as our sanitizer for all of our pools.
However, we do it differently than anyone else I've seen.

We have two tanks per pool house. One tank is a mix tank and one is a draw tank.
Into the mix tank we add 1oz cal hypo per 1 gallon of water. These are 100g tanks. Once everything is mixed and a few hours have passed for the sediment to settle to the bottom, we siphon the cal hypo mixture from the mix tank into our draw tank.
From the draw tank it gets fed into our bodies of water through chemical feeders and chemical sensors (we are using chemtrol ORP and pH).

Here are my questions:

1. The cal hypo clearly states to not pre-disolve, yet we do. Can I get an explanation of why you wouldn't want to dissolve before adding to your pool from a chemical standpoint? I have a feeling we are making the cal hypo not as effective but I do not have the chemistry background I'd need to understand the chemical process that could be happening by dissolving it first.

2. We go through a whole bunch of it. I have gone through all of our pool orders for 2018 and we went through 4000 lbs of cal hypo. At the dilution rate we use, that's 64000 gallons of liquid calhypo/chlorine. Does that not seem like an astronomical amount of chlorine for the amount of water we have? Dont even get me started on the CH.

3. Clearly if we were to switch off of cal hypo to liquid chlorine it would have to be much more potent because 64k gallons of chlorine would be a nightmare. Which is what leads me to believe we aren't getting the full potential from our cal hypo by pre mixing it

4. I want to switch to SWGs for all our bodies of water. The owner is the one who isnt quite for it. We live at the beach so we are already very much aware of the corrosive effects of salt. Our large spa and our largest pool is surrounded by an aluminum structure/building which has shown signs of corrosion over the years. He is convinced that a salt water pool would compound this issue greatly. I am not as convinced and think that the issues we see from using cal hypo are much greater. The other bodies of water are outside open air and aren't a concern as far as corrosion.

5. What would you do if you were in my shoes? Switch to swg? Switch to liquid? Other options?

Thanks everyone for your time.

-Brandon
 
Additionally, I realize at 1oz to 1g of water is a low ratio according to what the cal hypo container suggests by a large factor, it's just even when weve tried to up the ratio to 2oz to 1gallon of water weve had massive amounts of sediment build up in the mix tank.
 
Short answer - you're creating weakly concentrated hypochlorite solutions. Find a better way.

Long answer -

What you're doing is the "old school" method of using cal-hypo. Depending on the mix water being used, the cal-hypo is added to the mix tank and a good amount of the calcium hardness is allowed to precipitate out of solution so that you add a minimal amount of calcium with the hypochlorite. Via the "common-ion effect", the excess calcium added to the mix tank causes most of the calcium found in the powder (calcium oxide, calcium carbonate, sodium sulfate and calcium hypochlorite) to precipitate out. The "liquor" that is transferred to the holding tank is mostly just water, salt and calcium hypochlorite solution. If one added cal-hypo powder directly to a pool, you can expect to get about 6ppm CH increase for every 10ppm FC added. With your method, the CH increase will be less than that.

However, there is a problem - the pH of the resulting liquor is often uncontrolled and, when hypochlorite is dissolved into low pH water (low pH being less 11.5), the hypochlorite ion is very unstable and it will decompose into oxygen and chloride salt. So, if I had to guess, the % hypochlorite in solution in that holding tank is probably very weak in comparison to what you get bottled in the pool store as liquid chlorine (sodium hypochlorite). There are "bleach" test kits available that can be used to test the liquid in the holding tank for the % hypochlorite in solution so you can actually know what you're making. Then you can adjust your mixing procedures to better optimize your cal-hypo usage. Again, you'd typically want to make sure that the pH of liquid in the holding tank is high enough to stabilize the hypochlorite or else everything you make will simply decompose rapidly.
 
Thank you for the reply.
The pH of the solution once it's been siphoned over is in the high 9s to low 10s. However we are just using city tap water to mix the cal hypo. In our case this is usually around a 7.7. So what you are saying if I'm understanding correctly is that the cal hypo will be decomposing rapidly by using the city tap water to mix it? If so, is there even a viable work around to that?

I personally do not like using cal hypo and think there are better choices I just need more ammunition to come at the owner with.
But it is interesting to hear that this is an old way of doing it I had never heard of this being done before by anyone else around me.

My last question if you dont mind....
The slurry that settles to the bottom, is that mainly going to be calcium and other junk from the city tap water or is there potential to still be quite a bit of cal hypo/cl in the sludge?

Thanks again

-Brandon
 
I will be buying the hypochlorite test you recommended. I am very curious about what we are actually making. All that I see specifically mention sodium hypochlorite but I imagine it would do just fine with cal hypo too correct?

-Brandon
 
Upon closer examination of OP thread, It appears he is operating a system that I have never seen mention here. Though these are not large pools.

Who manufactured your system, is it “on line” remotely monitored or are these old school “fall out” feeders.

NSPF is restructuring , under apsp umbrella ?
 
Sark said:
Thank you for the reply.
The pH of the solution once it's been siphoned over is in the high 9s to low 10s. However we are just using city tap water to mix the cal hypo. In our case this is usually around a 7.7. So what you are saying if I'm understanding correctly is that the cal hypo will be decomposing rapidly by using the city tap water to mix it? If so, is there even a viable work around to that?

I personally do not like using cal hypo and think there are better choices I just need more ammunition to come at the owner with.
But it is interesting to hear that this is an old way of doing it I had never heard of this being done before by anyone else around me.

My last question if you dont mind....
The slurry that settles to the bottom, is that mainly going to be calcium and other junk from the city tap water or is there potential to still be quite a bit of cal hypo/cl in the sludge?

Thanks again

-Brandon
Click to expand...

See this technical link (specifically Slide #18) - Understanding Bleach Degradation

Below a pH of 10, the rate constant for hypochlorite degradation into oxygen, chlorate and chloride salt goes "through the roof". So if your holding tank has a pH in the 9's, you are essentially creating mostly salt water with a little bit of bleach in it. This is the reason why you are adding thousands of gallons of this mix to your pools every year and why you are not getting much bang for your buck. If you actually created a proper chemical mixture, you could easily cut your cal-hypo usage by a significant fraction....

The way to adjust pH would be to add something like caustic soda (lye, aka, sodium hydroxide) to the reaction tank so that the hypochlorite solution is stabilized. Lye is pretty dangerous stuff and should not be handled in a trivial manner as it can cause severe burns of skin tissue, eyes and mucous membranes. Normally these types of reactions are done with properly designed chemical handling systems that use appropriate engineering controls to ensure safety....this kind of stuff cannot be done on the cheap in an equipment shed. I'm not trying to be harsh, but you should really try to convince the person that owns these pools that what your doing is a waste of money, time, and potentially hazardous.

This method is "old" because it is what my Italian grandmother used to do in the 30's and 40's when washing clothes....powdered cal-hypo is originally known as "bleaching powder" or "chlorine powder" because it was what most people used in their homes to bleach clothes with. They would do just as you do, add a few tablespoons to a jug of warm water, let it sit and then decant the liquid into their washing bins to bleach and clean clothing. It was nasty work that resulted in more than it's fair share of personal injuries and one of the many reasons why liquid chlorine bleach (sodium hypochlorite) was considered so revolutionary to the housewife that didn't have to risk injury anymore when washing the family clothes....

The sludge at the bottom is mostly calcium carbonate with some calcium sulfate too (if the cal-hypo has sulfates in it). It occurs because the addition of the cal-hypo into hard water (water that contains carbonate alkalinity) drives up the calcium concentration and the pH to a point well beyond the solubility limit and so the calcium falls out of solution as a carbonate. In fact, at some point, you can exhaust the carbonate concentration in the fill water to just below the solubility limit and, if you were to add more carbonate with something like baking soda, you would precipitate out even more calcium. Again, what you're doing is a very uncontrolled chemistry experiment, so there's lots of competing reactions going on. One thing is for sure though, you are adding chlorine to your pools in just about the least efficient way possible ;)

Good luck trying to convince the owner...I find that these people that don't have to deal with the issue day-to-day have very little incentive to change as they take the standard "if it ain't broke, don't fix it!" attitude....usually that attitude gets corrected when someone files a personally injury lawsuit and/or the local authorities are called in to shut down unsafe business operating practices....
 

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PoolguyinCT said:
Who manufactured your system, is it “on line” remotely monitored or are these old school “fall out” feeders.
Click to expand...
Not sure exactly what you are asking here but there is no "system" in use here. We simply create our own bleach solution (albeit poorly) and use automated chemical feeders in conjunction with ORP and pH sensors to pump acid and Cl into our water as needed.

The chemtrol get set to an ORP setpoint that we determine, and when the orp sensor senses that it's not at this setpoint, it signals the Cl feeder to add Cl to the water. Same goes for pH. It's very simple and effective stuff. What is clearly not effective in this scenario is our source for Cl.

-Brandon
 
Thank you joyful, I dont see you coming off as harsh I want all this info. I very much care about my pools and this business that the owner has going here. I just want to improve things.
The main being that I don't like me and my guys handling cal hypo. I am already against it I just wanted to make this a logical argument with the owner, not an emotional one. And since you have given me quite a bit of knowledge and info to bring to the table, I thank you.

And trust me, I dont want to make this whole calhypo situation work. I just was interested in what's involved in potentially making it work. For arguments sake with the owner.

I will say that since I've been here the owner has been very open to change and I have made quite a few good changes to the pool systems here. And he is not an owner who doesnt care about his property for his operation. He is nearly 80 though so that very well could be where this "method" comes from. But in his defense it has worked for decades and the health dept has always rated our pools perfect and complimented our team on our competency and understanding. It's amazing how the average home pool owner on this site knows more than most commercial pool people I've met in this industry.

Anyways I'm rambling. Like I said my main goal was to gather as much information as I could to incite a change. And I thank everyone who has helped me in that endeavor.

Please, if anyone has anything more to add, or questions of me, don't hesitate.

-Brandon
 
A properly sized sodium hypochlorite (liquid chlorine) tank would be an easy fit into your system and there are many bulk manufacturers that can do safe and effective deliveries and transfers of liquid chemicals. Properly manufactured sodium hypochlorite solutions, when stored appropriately, have shelf lives of many months and you could easily manage the supply and demand of the system. Liquid chlorine injection is very easily accomplished and tying it into to an ORP controlled automation system is pretty basic. A good manufacturer of commercial pool equipment probably has a turn-key solution available. Liquid chlorine would be safer to handle as you really wouldn't be handling it and the engineering controls to prevent spills are pretty easy. From a chemistry perspective, you add less "extra stuff" that pool water doesn't need, namely calcium-hardness. Since liquid chlorine is sodium hypochlorite, you are only adding sodium ions which do not contribute in any way to scale formation. The amount of excess salt added by liquid chlorine is minimal and you're adding salt anyway with cal-hypo. Finally, liquid chlorine is a pH neutral (or pretty darn close to neutral) chemical addition while cal-hypo strongly increases pH since it contains a lot of calcium hydroxide.

The issue is cost. The way you are doing it now costs very little (until an accident happens and someone gets hurt) while a new chlorine injection system with all of the regulatory sign offs and engineering controls will have a significant fixed cost. However, going forward the cost of that installation should pay for itself over time with less work on your part as the managing pool operator AND you will likely save on chemistry as the liquid chlorine will give you much better FC bang for the buck you spend on it.
 
I could be wrong, but I wouldn't concerned about the corrosive effects of a saltwater generator near the ocean. You already have a ton of salt in the air there (which certainly does lead to corrosion) and your pools already probably have a salt level close to 1500 ppm. I think raising the levels to 3000 ppm would be the least of your worries.
 
You're correct our indoor pool surrounded by the aluminum structure is around 1200 ppm salt.
I will be bringing all this info to the owner at the end of the week so hopefully we will see a change. Thanks so much to everyone so far.

-Brandon
 
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