Calcium Hypochlorite powder vs NST tablets

Zook13

Silver Supporter
Apr 13, 2020
7
Tucson, Arizona
Pool Size
11000
Hello,
We have a new (to us) home in Tucson AZ with a 11,000 gallon pebble tec pool. When I first moved in a friend helped me with the chemicals but we quickly learned that the CYA was above 120 so last month I drained the pool and restarted. I believe that the former owner had used the stabilized tablets (dichlor/trichlor?) exclusively and this caused the high CYA.

Ok, now for the question: I want to make sure my pool does not drift into high CYA again. For now I have been using them to actually bring up my CYA and bring down my Ph and this has been working well. I'm right about where I want to be now for the levels and want to know what the "Braintrust" thinks about the use of the four chlorine types:
  1. Diluted chlorine liquid (walmart, etc)
  2. Stabilized tablets (dichlor/trichlor)
  3. NST tablets which are ~ 70% Calcium Hypochlorite
  4. Calcium Hypochlorite powder (~ 70%) .

  • Keeping in mind that I am concerned about the stabilized tablets but I understand that they will work well when I travel I would like to refrain from using them for normal maintenance.
  • The NST tables are very expensive and when I compared the active ingredients the NST Tablets are ~ 70% Calcium Hypochlorite.
  • Why not just buy the powdered Calcium Hypochlorite (like Power powder plus from Leslie's) or (CALCIUM HYPOCHLORITE POOL SHOCK BUCKET from inthewswim.com. Then I could use my Stabilized tablets (dichlor/trichlor) when I'm on vacation?
With the powdered Calcium Hypochlorite I figure for my 11,000 gallon pool I will need ~12 ounces for each dose. With 50lbs it should be about 66 doses at a cost of about $2.25 each dose.

The NST Tables are 10.5oz each. A 24.5lb Bucket of them gives you approximately 37 tablets. At $125 for that 24.5 lb bucket you are paying ~ $3.37 per dose.

Can anyone shed some pros and cons of these?

Thanks much
Rob Z
 

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mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
37,031
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Welcome to the forum!
As you live in Tucson, I suspect you have hard water. So using Calcium Hypochlorite will make your pool water calcium hardness levels go very high very quick. Can you post a full set of test results from your own test kit?
Your solution is to exclusively use liquid chlorine. Or, install a SaltWater Chlorine Generator.
I suggest you read ABC's of Pool Water Chemistry.
 
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JJ_Tex

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Bronze Supporter
Jul 17, 2019
2,316
Prosper, TX (DFW)
Pool Size
13000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
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Liquid chlorine is king around here because it simply adds chlorine.

As you have found out solid forms of chlorine also add either CYA (dichlor/trichlor products) or Caldium (Cal-Hypo products). Both CYA and Calcium will build up in your water and force you to drain to manage the levels down.

Additionally, we have lots of members in the Southwest and all seem to have high levels of calcium in their fill water assuming they do not fill with a water softener.

Welcome to TFP and make sure you take a look at Pool School, including an article on the types of chlorinating:
 
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Zook13

Silver Supporter
Apr 13, 2020
7
Tucson, Arizona
Pool Size
11000
Liquid chlorine is king around here because it simply adds chlorine.

As you have found out solid forms of chlorine also add either CYA (dichlor/trichlor products) or Caldium (Cal-Hypo products). Both CYA and Calcium will build up in your water and force you to drain to manage the levels down.

Additionally, we have lots of members in the Southwest and all seem to have high levels of calcium in their fill water assuming they do not fill with a water softener.

Welcome to TFP and make sure you take a look at Pool School, including an article on the types of chlorinating:
Thank you, this is helpful.
 

Zook13

Silver Supporter
Apr 13, 2020
7
Tucson, Arizona
Pool Size
11000
Welcome to the forum!
As you live in Tucson, I suspect you have hard water. So using Calcium Hypochlorite will make your pool water calcium hardness levels go very high very quick. Can you post a full set of test results from your own test kit?
Your solution is to exclusively use liquid chlorine. Or, install a SaltWater Chlorine Generator.
I suggest you read ABC's of Pool Water Chemistry.
Thank you, I have been avoiding reading the ABC's....puts me to sleep every time. So much information to go through.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
37,031
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
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scdaren

Gold Supporter
Bronze Supporter
May 20, 2018
465
Clovis, CA
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
Those results look good BUT those test strips tend to be very inaccurate / imprecise. You'll want to invest in a higher quality test kit like a TF-100 or a Taylor K-2006C. It's hard for us to give advice based on those strips (known around here as "guess"strips) because it's difficult to know whether they are correct.

As others have said, stick to liquid chlorine or get a saltwater chlorine generator. The Cal-Hypo is okay for places that get a lot of rain and/or have vinyl pools, but in the drier and desert climates they'll make your calcium levels go through the roof, which imo is worse that CYA. An algae bloom can be dealt with - hardwater stains from calcium buildup are much more difficult to deal with.
 
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Zook13

Silver Supporter
Apr 13, 2020
7
Tucson, Arizona
Pool Size
11000
Those results look good BUT those test strips tend to be very inaccurate / imprecise. You'll want to invest in a higher quality test kit like a TF-100 or a Taylor K-2006C. It's hard for us to give advice based on those strips (known around here as "guess"strips) because it's difficult to know whether they are correct.

As others have said, stick to liquid chlorine or get a saltwater chlorine generator. The Cal-Hypo is okay for places that get a lot of rain and/or have vinyl pools, but in the drier and desert climates they'll make your calcium levels go through the roof, which imo is worse that CYA. An algae bloom can be dealt with - hardwater stains from calcium buildup are much more difficult to deal with.
Thanks, those things look like you need a PhD to read them. I expect I don't need all of the tests but it sounds like hardness, specifically calcium is one I want to watch.
 

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mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
37,031
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Hi Marty, thanks for the help. I have updated my signature and here is a picture of my test results.
Thank you for the signature.
As scdaren mentioned, you need a proper test kit. I suggest the TF100. A proper test kit is needed to get the accurate water chemistry results needed to follow the TFP protocols.
We will not provide any guidance based on test strips or pool store tests.
 

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scdaren

Gold Supporter
Bronze Supporter
May 20, 2018
465
Clovis, CA
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
Thanks, those things look like you need a PhD to read them. I expect I don't need all of the tests but it sounds like hardness, specifically calcium is one I want to watch.
Lol not at all. It's actually WAY easier to count drops than it is to decipher some of those color of the rainbow in my opinion. If you want to diy your pool and do it right, and if you want to get advice from people here, getting a proper test kit is absolutely necessary.
 
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scdaren

Gold Supporter
Bronze Supporter
May 20, 2018
465
Clovis, CA
Pool Size
15000
Surface
Plaster
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Thanks, those things look like you need a PhD to read them. I expect I don't need all of the tests but it sounds like hardness, specifically calcium is one I want to watch.
You are better off ordering a TF-100 from these guys than from Amazon. Same reagents, just repackaged. The Speedstir makes things a lot easier as well. TF-100 Test Kit ™
 

scdaren

Gold Supporter
Bronze Supporter
May 20, 2018
465
Clovis, CA
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
I noticed that MKNAUSS also wrote Speedstir (like you) but on the site it lists a Smartstir.....is this what you are talking about?
Yeah, same thing, looks like they changed the name, maybe a different model or something.
 
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proavia

LifeTime Supporter
TFP Guide
Feb 6, 2015
2,121
Chandler AZ
Pool Size
12300
Surface
Plaster
Chlorine
Liquid Chlorine
For liquid chlorine, do you have an E-konomy Pool near you? I believe they carry HASA 12.5% liquid chlorine in refillable 4 gallon pack... four 1 gallon jugs in a carrier (you pay a one time deposit on the carrier and 4 jugs). You may find it's more cost effective to buy fresh 12.5% from them than the 10% Pool Essentials from Walmart or HD.

As for a test kit, the TF100 is the way to go. Add the Speedstir/Smartstir. You DO need all the test options included with the TF-100... not everyday, but you do need to use all the options monthly. Using the drop based tests are easy once you do them a couple of times. As Marty stated, we won't offer guidance based on test strips or pool store results - they have proven to be unreliable and inconsistent time and time again.

Stay far away from Calcium Hypochlorite - it adds calcium to the water. In the desert southwest, our water is already high in calcium. Based on where in Tucson you are located, your tap water CH might be 200-250 or greater out of the tap. As water evaporates, the CH stays behind. Add more water and the CH increases. Your CH can easily double in the course of a year just adding water to your pool (without the use of CalHypo).
 
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Zook13

Silver Supporter
Apr 13, 2020
7
Tucson, Arizona
Pool Size
11000
For liquid chlorine, do you have an E-konomy Pool near you? I believe they carry HASA 12.5% liquid chlorine in refillable 4 gallon pack... four 1 gallon jugs in a carrier (you pay a one time deposit on the carrier and 4 jugs). You may find it's more cost effective to buy fresh 12.5% from them than the 10% Pool Essentials from Walmart or HD.

As for a test kit, the TF100 is the way to go. Add the Speedstir/Smartstir. You DO need all the test options included with the TF-100... not everyday, but you do need to use all the options monthly. Using the drop based tests are easy once you do them a couple of times. As Marty stated, we won't offer guidance based on test strips or pool store results - they have proven to be unreliable and inconsistent time and time again.

Stay far away from Calcium Hypochlorite - it adds calcium to the water. In the desert southwest, our water is already high in calcium. Based on where in Tucson you are located, your tap water CH might be 200-250 or greater out of the tap. As water evaporates, the CH stays behind. Add more water and the CH increases. Your CH can easily double in the course of a year just adding water to your pool (without the use of CalHypo).
Thanks Gene, this is helpful. We do have an E-Konomy here and they are the ones I trust the most. Too much bad and contradicting info at Leslies. I will go there and ask about the refillable 12.5% chlorine containers, this sounds like a great solution.

Rob