Can adding a lot of calcium chloride at once reduce FC??

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B

Bobkam

0
Jun 22, 2013
4
Southborough, MA
I have been a vinyl pool owner for 3 years now, and each year I have tried to tackle a balancing issue. Last year I tackled CYA (I had near 0 and was losing FC rapidly during the day). I used a conditioner to increase CYA to about 50-60, and FC problem solved.

This year, I am tackling calcium hardness. CH has always tested at about 40ppm using my Taylor K-2006 kit. Yesterday, I broadcast about 25lbs of "Pool Mate Calcium Increase for Swimming Pools" (made by Robelle). It all dissolved very quickly, no cloudiness or white residue. Immediately prior, I tested FC at about 3.0 ppm.

Good news this morning is CH is testing at a much more reasonable 240 ppm. Bad news is FC is down to 0.6 ppm!!

I have an SWG (Pentair IC-40) that I generally run at about 40% capacity 24/7 during the summer (next year's project is getting off 24/7!). I checked CYA again this morning and it is around 60ppm, so that's not the culprit for the FC loss. I don't see any algae or organic growth. I jacked up the SWG to 70% output about 3 hours ago, and as of yet, no change in FC.

My question is: Can adding 25lbs of calcium chloride at once have a short term impact on FC?

Alternatively, could my SWG be going (I probably have over 10,000 hours on it and have never acid washed)?

Thanks!
 
Welcome to TFP!

Calcium shouldn't have any effect of chlorine. No real need to add it either with a vinyl liner.

At 60ppm CYA you were right at the minimum FC level and a little glitch could have dropped your chlorine to where algae has gotten started consuming your chlorine.
 
25lbs of Calcium Chloride in your pool size 28k
should have only raised your CH ~100ppm with a staring point of 40 that means your testing or pool size estimation is off.

There is no reason to raise the CH in a vinyl lined pool - you can only get rid of it with water change out.

Take a few swims and see how crusty your hair feels after swimming vs. what it was before
 
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Thanks guys. Pool is vinyl, but we have stone pavers on deck and coping. I had read that soft water would seek out stone and grout and possibly pit pavers, but it sounds like you guys think I didn't need to increase CH. Good news is our water is so soft, that CH will continue to drop as I add water due to evaporation, so I can just let it decrease back to where it was (it's only at about 220 ppm right now).

FC is up to 3.0 again this morning, but only after I cranked SWG up to 90% about 12 hours ago (usually run at 40%). Don't see any signs of algae. I'll test FC again a midday.

Interesting point on the FC minimum John. I had always assumed desired FC range is between 2.0-4.0. But using the minimum FC of [4.5% x CYA] from the CYA/Chlorine chart (with an SWG) and assuming CYA of about 50-60, the minimum FC should be about 2.25-2.70. Sounds like I should increase FC closer to 4.0 rather than 3.0.
 
Bobkam said:
CH will continue to drop as I add water due to evaporation, so I can just let it decrease back to where it was (it's only at about 220 ppm right now).
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CH does not evaporate, it stays behind in the bulk pool water. CH, like CYA only lowers when you pump water out of the pool, water is splashed out of the pool or it is carried out of the pool with wet bating suits and wet dog fur.
 
How much Pool School have you read? Start with these:
ABCs of Water Chemistry
Recommended Pool Chemicals
How to Chlorinate Your Pool

The other thing I want to point out is - don't be too concerned chasing "perfect" numbers. Pool stores love to have you chasing numbers by selling you multiple products to raise this, lower that.

Learn your pool an understand what it likes. Once you have the pH in range, the chlorine is at a sufficient level as compared ot the CYA and the water is clear anything else can be a slow go. No hurries.
 
tim5055 said:
How much Pool School have you read? Start with these:
ABCs of Water Chemistry
Recommended Pool Chemicals
How to Chlorinate Your Pool
Click to expand...

Thanks Tim. I have read the articles in pool school, and have been able to keep the pool well balanced for the first three years. The recent drop in FC was pretty sudden, leading my original question whether or not it had anything to do with adding the Calcium Chloride (I understand from prior responses above that this is not the case)

I guess my only other causes are (1) losing FC in sun due to not enough CYA, (2) SWG is losing efficiency (it has over 10,000 hours and has never been acid washed) or, (3) an algae issue. No signs of algae, and pump runs 24/7 keeping lots of flow in the pool.

FAS-DPD test shows FC has dropped again today from 3.0 early this morning to 2.0 just now, with SWG running at 90% (usually runs at 40-50%). I'm getting more Taylor CYA reagent to retest CYA to see if it has dipped too low. Hopefully I will have enough FC by the end of the day to try an OCLT test tonight.

Am I missing any other possible causes?
 

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I realize this is an old thread but I can add that adding 25lbs of calcium chloride to an 18.5k gallon pool does, in fact, obliterate the chlorine from about 5/6ppm to zero.
I read somewhere on another thread that increasing CH might have that affect on FC so had the pump run overnight to generate FC through the swg and to continue to help with mixing the calcium chloride. I checkEd FC this morning and that’s when I got the zero result. Cya is about 50.
I’ve since added a gallon of FC this morning and kept the pump/swg running. I’ve checked again just now and FC is at 2.5ppm So added another gallon of fc and have left the pump running.

we did have a massive storm last night and what looked to be a torrential downpour so we lost some water to overflow. But still, holy fc depletion, bat man!

plus, maybe add calcium chloride in stages next time.
 
BritDan said:
I realize this is an old thread but I can add that adding 25lbs of calcium chloride to an 18.5k gallon pool does, in fact, obliterate the chlorine from about 5/6ppm to zero.
I read somewhere on another thread that increasing CH might have that affect on FC so had the pump run overnight to generate FC through the swg and to continue to help with mixing the calcium chloride. I checkEd FC this morning and that’s when I got the zero result. Cya is about 50.
I’ve since added a gallon of FC this morning and kept the pump/swg running. I’ve checked again just now and FC is at 2.5ppm So added another gallon of fc and have left the pump running.

we did have a massive storm last night and what looked to be a torrential downpour so we lost some water to overflow. But still, holy fc depletion, bat man!

plus, maybe add calcium chloride in stages next time.
Click to expand...
Just found this thread. I added 20lb calcium chloride yesterday to a 25K gal pool with a pentair SWG. Normal FC yesterday and none today, even at the jets at 100%, with all green lights on the generator. Did you figure out why adding the calcium chloride dropped the chlorine production? How long did it take to go back to normal. Wondering if it precipitated on the electrolysis plates and needs to be cleaned off.
 
I’ve added quite a bit of calcium to my pool once or twice and did not find any noticeable difference in chlorine. Both of these cases sound like the chlorine is already too low of it’s only 3ppm and an additional problem of using pool store testing as evidenced by the 2.25-2.70 results mentioned above.
 
Been adding to my hardness, and I've read that here: Calcium Hardness - Further Reading

Adding Calcium Chloride May Reduce FC to 0​

Over the years there have been reports of members finding their FC at 0 after adding calcium chloride. There is no chemical explanation for this but the fact is it is happening.

Check your FC often after adding calcium chloride and add liquid chlorine if you see it drop.
 
Bperry said:
I’ve added quite a bit of calcium to my pool once or twice and did not find any noticeable difference in chlorine. Both of these cases sound like the chlorine is already too low of it’s only 3ppm and an additional problem of using pool store testing as evidenced by the 2.25-2.70 results mentioned above.
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Thanks. It’s odd that the SWG is not putting out chlorine after adding the calcium chloride, despite all the lights being green. Salt level is good. Flow is good.
Any thoughts on why? I would expect the cell light to flash if there was precipitation on the electrolysis plates. Is there interference with test reagents and strips? I agree my FC starting point was low, but why no chlorine at the jets?
 
Braf said:
Thanks. It’s odd that the SWG is not putting out chlorine after adding the calcium chloride, despite all the lights being green. Salt level is good. Flow is good.
Any thoughts on why? I would expect the cell light to flash if there was precipitation on the electrolysis plates. Is there interference with test reagents and strips? I agree my FC starting point was low, but why no chlorine at the jets?
Click to expand...
In any case, don't wait for the SWCG to "catch up". Add liquid chlorine to get to your targe FC level.
 
Braf said:
Thanks. It’s odd that the SWG is not putting out chlorine after adding the calcium chloride, despite all the lights being green. Salt level is good. Flow is good.
Any thoughts on why? I would expect the cell light to flash if there was precipitation on the electrolysis plates. Is there interference with test reagents and strips? I agree my FC starting point was low, but why no chlorine at the jets?
Click to expand...
It’s possible it’s outputting chlorine but it’s just being consumed. I think the advice is if you do add calcium to do it slowly and in small amounts to avoid cloudiness. Don’t use test strips for anything, not worth the time.
 
I’ve personally experienced adding 8lbs of hardness increaser also bring my fc from 4 to 0 in a 21,500 gallon pool.

I have a salt water gen that runs 8am-8pm. I checked fc around 8pm and it was around 4.5. I dumped in 8lbs of hardness plus. I ran the pump for a couple hours to circulate it.

Next more fc was around 0.5.

It wasn’t killed by sunlight because overnight. I hadn’t lost anywhere near that fc overnight before or since.

The ONLY thing it could have been - from my point of view - was the calcium.

Note: I’ve had this pool for less than 2 months but I’ve been very diligently testing daily and learning the tfp ways.
 
I’ve also observed reduced FC after adding calcium chloride. From what I was ever able to find, made no sense for that to happen.

The only thing that comes to mind is possibly an impurity in the calcium chloride effects FC. Calcium chloride can be obtained using the Solvay Process, which involves ammonia, which is later extracted. I’d wonder if there might be trace amounts of an ammonia compound (or perhaps something else) in some brands of the CaCl2 which would explain the reduction in FC?

easychem.com.au

The Steps Used in The Solvay Process - EasyChem Australia

Identify, given a flow chart, the sequence of steps used in the Solvay process and describe the chemistry involved. Free HSC Chemistry study notes.
easychem.com.au

edit to add — and therefore, out of an abundance of caution, it may make sense to monitor FC after adding calcium chloride (and really, maybe after adding anything — who knows what trace contaminates might be in anything so if the cautious type (like me), keep an eye on things just in case).
 
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