When are chemicals not just chemicals?

[Old Guard]

My 30,000 gallon, 91°F Therapy Pool has been a little low on the calcium hardness scale since I took it over. It has also been a bit cloudy. The first time I dosed it with 25 lbs of calcium chloride (which I purchased from my local pool chemical supplier) the water miraculously became crystal clear and a large amount of sediment appeared on the bottom overnight. A month later, I ordered a second bag of calcium chloride from the same supplier. I dumped in another 25 lbs. The next day FC was zero (started at 4). It took 1½ gallons of very strong liquid chlorine to make it swimmable again. A scan of the QR code on this second bag revealed that it was intended for use in the oil field.

Now I am gun shy. I need to order 1.300 pounds of this stuff to treat all five of my pools. My new industrial chemistry supplier plans to ship me Dow Flake which is 94% calcium chloride, 4% lead and the rest other scary things like fluoride and magnesium. Looks like it was intended to melt I ice on pavement. Should I put this stuff in my pools?

 

[Texas Splash]

Below is from our Recommended Chemicals page if it helps.

Calcium hardness can be raised with calcium chloride or calcium chloride dihydrate. They are available in some areas as Peladow, Dowflake, Tetra Flake, or Tetra 94, often sold as a deicer by hardware stores, and some big box stores, in colder climates. Pool stores will carry either calcium chloride or calcium chloride dihydrate under a variety of names, including Hardness Plus, Balance Pak 300, Calcium Hardness Increaser, etc. Calcium products should be spread across the surface of the deep end of the pool.

Recommended Pool Chemicals

Which should I buy? TFP's recommended pool chemicals are cheap, easy, and won't unbalance your pool water.

www.troublefreepool.com

 

[JoyfulNoise]

4% lead ?!?! Who the heck would even use that for road de-icing ?? That would cause toxic runoff.

Put it in your pool?? I think the answer is obvious …. NO.

 

[duraleigh]

My 30,000 gallon, 91°F Therapy Pool has been a little low on the calcium hardness scale since I took it over. It has also been a bit cloudy. The first time I dosed it with 25 lbs of calcium chloride (which I purchased from my local pool chemical supplier) the water miraculously became crystal clear and a large amount of sediment appeared on the bottom overnight.

Don't attribute the addition of Calcium Chloride as having cleared your pool........it doesn't do that. Since sediment dropped out, I would suspect the addition of chlorine as the reason your pool cleared.

 

[Old Guard]

4% lead ?!?! Who the heck would even use that for road de-icing ?? That would cause toxic runoff.

Put it in your pool?? I think the answer is obvious …. NO.

Sorry. My chemistry incompetence rears its ugly head again. My chemical supplier sent me this:

That's <4 PPM right? Should I still be concerned? I need to pull the trigger on buying a whole bunch of this stuff from someone.

 

[JoyfulNoise]

What is the source material’s intended use? Is it used for swimming pools or some other purpose?

<4ppm could just mean that whatever detection method they were using isn’t sensitive to levels lower than that. The EPA drinking water standards are far lower - less than 15 parts per BILLION. And even the EPA concedes that medical science clearly shows that any detectable level of lead, even down to parts per trillion levels, is not good for human health.

 

[Old Guard]

Don't attribute the addition of Calcium Chloride as having cleared your pool........it doesn't do that. Since sediment dropped out, I would suspect the addition of chlorine as the reason your pool cleared.

For the last month, the only chlorine that intentionally goes into any of my Flowood pools is "12½ Sodium Hypochlorite" that comes from a chemical supplier in 55-gallon drums. We test the water 3X per day for chlorine and pH. I should have recorded what I put in the first time to increase CH but I did not. It did increase CH by he expected amount an unexpected precipitate that covered at least 10% of the pool bottom overnight. Did that twice. Didn't seem to impact chlorine levels at all. When I put in this last batch (purchased from the same pool company) it sucked ALL of the chlorine out of the pool, produced a negligible increase in CH, and left the water a little cloudy.

 

[Old Guard]

What is the source material’s intended use? Is it used for swimming pools or some other purpose?

<4ppm could just mean that whatever detection method they were using isn’t sensitive to levels lower than that. The EPA drinking water standards are far lower - less than 15 parts per BILLION. And even the EPA concedes that medical science clearly shows that any detectable level of lead, even down to parts per trillion levels, is not good for human health.

It seems it is used primarily to melt ice, secondarily to accelerate the curing of concrete.

 

[JoyfulNoise]

Adding large amounts of calcium chloride to water is always fraught with difficulty. First, it is rarely a pure material but often has significant contaminants in it like calcium sulfate, carbonates and oxides. It can also contain magnesium chloride and magnesium carbonate. Finally it can have significant amounts of sand and grit in it.

Calcium chloride by itself is highly exothermic when it hydrates as anyone that has held it in their hands can attest to (don’t do it, it will cause skin burns). It is deliquescent, meaning that water enters and dissolves INTO the solid material up to its solubility limit before it mixes into the bulk water volume. This can cause very localized heating to the point of almost boiling the water around it. Mechanical agitation and mixing is extremely important.

Large amounts of calcium chloride will react with the carbonate alkalinity in water forming a fine precipitate of calcium carbonate that will not redissolve. This is what leads to cloudiness and fine precipitation on the floor of a pool. That calcium leaves the water and does not contribute to CH.

We don’t have a good explanation for why some CH additions cause the free chlorine levels to drop but it is something that we have seen reported. It doesn’t happen all the time. I believe it is due to some undisclosed contaminant in the CH Increaser mix, either naturally occurring or some additive such as an anti-caking agent. And it is this impurity that leads to increased FC demand.

It seems it is used primarily to melt ice, secondarily to accelerate the curing of concrete.

Then it should not be used in swimming pools. You should find a different supply.

 

[Old Guard]

I put 100 pounds of CalChlor brand calcium chlorite (83-87% flakes) in a 125,000-gallon pool yesterday evening. It got about 7 gallons of chlorine from my pump overnight. This morning it tested 0% FC. I turned the pump back on and poured in 2 gallons of 12½%. The opening guard reported 0/0 at 1300 even after putting in 2 more gallons. I thought she was daft and ran right over. She was absolutely right. 6 gallons later we were at 1 FC 2 TC. What is this all about?

Last night I also put 100 pounds of the same stuff in my 400,000 gallon pool. It also measured 0/0 this morning. I put in 8 gallons of freshly decanted 12½ and it came out FC of 2.

 

[JoyfulNoise]

Well … seems like an ammonia problem. If you’re adding chlorine and the FC is staying zero and then you start to see both CCs and FC, then that looks like ammonia. There is no interaction chemically between active chlorine (hypochlorous acid/hypochlorite) and calcium chloride. We have gotten many reports of people adding hardness increaser and their FC goes to zero. Not sure what to say there except that there must be some secondary effect associated with the high heat of dissolution causing localized water boiling and maybe the neutralization of chlorine. However, one could test that theory by first dissolving all the calcium chloride in water and then adding the cooled liquid instead. Perhaps the calcium chloride granules had some undisclosed anti-caking/drying agent added. Some of those compounds would act as a reducing agent toward chlorine.