Numbers game help.

[kbp911]

Hello all, long time reader/learner.

Stats to start off with:

30k gallon salt water in ground pool.
PH 7.8
Chlorine 5.4
CC 0.2
ALK 110
CH 170
CYA 60

I haven't been very concerned with my CH level as I have a vinyl liner. For the last few seasons I have ran it wherever mother nature decided to put it (rain/snow/soft well water). I decided to start following the Langelier Saturation Index from
Pool Saturation Index Calculator | PENTAIR

I decided even though all the other numbers were on target to go ahead and increase the hardness from the old 60 (yes, I heard that gasp) and added 30lbs of CaCL2 over several days to bring it to the current 170 level.
My concern is now for whatever reason I can not keep chlorine in the pool at all. After adding the two dippers, the test water did not change color at all indicating a zero amount. I didnt think too much of it and added an entire bottle of 12.5% NaClO liquid chlorine bringing the amount up to around 5.0 and called it a day.
Today the same thing happened. It tested out at zero. I just got done adding another bottle of the liquid chlorine bringing it up to 5.4 which is the current level.
1) Does adding 30LBS of Calcium chloride eat/kill/not play well with chlorine? and
2) I know from measuring the pool it is about 30k gallons. According to all the charts adding that much of CaCl2 should not have added that much to the CH level.
3) Does adding the CaCl2 affect the salt level? I noticed it went from the normal 3200 PPM to 3300 PPM instantly after adding. (This is more of a chemistry question as the 'chloride' of Calcium Chloride I assume is the same as in NaCl only it has two atoms of chloride compared to only one)
4) Finally is the NaClO final 'O' one atom of oxygen making it sodium chloride and oxygen to form sodium hydrochloride?

To be honest I enjoy balancing the water and the chemistry that comes with this more than I do actually using the pool.

Thanks in advance!

Ben

 

[UN1017]

I don't think the unnecessary addition of calcium chloride had any effect on your FC levels. Clearly your SWG is either not working or it can't keep up. This just sounds like a classic case of needing a SLAM.

Out of curiosity...are you still running a T-15?

 

[UN1017]

By the way...using PoolMath, adding 30 lbs of calcium chloride to your pool should have raised your CH by 108, so your 170 seems right on. I'll leave the hard chemistry questions for chem geek.

 

[chem geek]

I decided even though all the other numbers were on target to go ahead and increase the hardness from the old 60 (yes, I heard that gasp) and added 30lbs of CaCL2 over several days to bring it to the current 170 level.
My concern is now for whatever reason I can not keep chlorine in the pool at all. After adding the two dippers, the test water did not change color at all indicating a zero amount. I didnt think too much of it and added an entire bottle of 12.5% NaClO liquid chlorine bringing the amount up to around 5.0 and called it a day.
Today the same thing happened. It tested out at zero. I just got done adding another bottle of the liquid chlorine bringing it up to 5.4 which is the current level.
1) Does adding 30LBS of Calcium chloride eat/kill/not play well with chlorine? and
2) I know from measuring the pool it is about 30k gallons. According to all the charts adding that much of CaCl2 should not have added that much to the CH level.
3) Does adding the CaCl2 affect the salt level? I noticed it went from the normal 3200 PPM to 3300 PPM instantly after adding. (This is more of a chemistry question as the 'chloride' of Calcium Chloride I assume is the same as in NaCl only it has two atoms of chloride compared to only one)
4) Finally is the NaClO final 'O' one atom of oxygen making it sodium chloride and oxygen to form sodium hydrochloride?

Our own PoolMath calculates the Calcite Saturation Index so you can use that and it may be more accurate and it will automatically adjust TA based on CYA and Borates.

Though you are getting zero FC, are you seeing CC? How quickly is it getting used up? The Calcium should not affect the FC unless there were terrible contaminants in it.

Calcium chloride does increase the salt level. The salt will increase by about 56% of the CH increase if the salt test is a chloride measurement (reported as ppm sodium chloride).

Sodium hypochlorite is NaOCl which when dissociated in water is sodium ion Na⁺ and hypochlorite ion OCl^- though about half of this at pH 7.5 becomes hypochlorous acid HOCl. I wouldn't call it sodium chloride and oxygen because the chlorine atom is not chloride, that is not in the -1 oxidation state. Instead it is in the +1 oxidation state similar to a hydrogen ion. In fact, hypochlorous acid H-O-Cl looks very much like water H-O-H except that one hydrogen is replaced with chlorine (and chlorine is a larger atom). Look at hypochlorous acid:

and compare it to water

 

[kbp911]

I don't think the unnecessary addition of calcium chloride had any effect on your FC levels. Clearly your SWG is either not working or it can't keep up. This just sounds like a classic case of needing a SLAM.

Out of curiosity...are you still running a T-15?

Yes I am still using the T15 except it is a brand new one. I take it you also stating that I did not need to add the calcium due to it being an vinyl liner? I was concerned for the metal parts inside the T15 as well as the propane heater. Thank you for your response!

- - - Updated - - -

Our own PoolMath calculates the Calcite Saturation Index so you can use that and it may be more accurate and it will automatically adjust TA based on CYA and Borates.

Though you are getting zero FC, are you seeing CC? How quickly is it getting used up? The Calcium should not affect the FC unless there were terrible contaminants in it.

Calcium chloride does increase the salt level. The salt will increase by about 56% of the CH increase if the salt test is a chloride measurement (reported as ppm sodium chloride).

Sodium hypochlorite is NaOCl which when dissociated in water is sodium ion Na⁺ and hypochlorite ion OCl^- though about half of this at pH 7.5 becomes hypochlorous acid HOCl. I wouldn't call it sodium chloride and oxygen because the chlorine atom is not chloride, that is not in the -1 oxidation state. Instead it is in the +1 oxidation state similar to a hydrogen ion. In fact, hypochlorous acid H-O-Cl looks very much like water H-O-H except that one hydrogen is replaced with chlorine (and chlorine is a larger atom). Look at hypochlorous acid:

and compare it to water

Thank you for your response also! This is what I was looking for to see exactly what was going on. I was seeing a very small amount of CC with a result of .02. I will retest today and see what is shows. I ran the SWG at 70% for the last 12 hrs last night so if I get another zero reading then the T15 must be bad. The only thing is I have never in the four years of having this pool, even in the worst bright sunlight conditions have I ever seen a loss of 4-5 PPM of chlorine in one night. This more than anything is what surprised me two days/nights in a row.

Thank you again for taking the time and responding.

Ben

 

[chem geek]

Did you mean a CC result of 0.2? That's the resolution of the FAS-DPD test using a 25 ml water sample and means <= 0.2 ppm so could be very close to zero. I wouldn't worry about that at all.

Loss of chlorine overnight means you have something consuming chlorine in the pool such as nascent algae growth. You generally deal with that by doing a SLAM to kill it off and then once you pass the Overnight Chlorine Loss Test you then maintain the proper FC/CYA level never going below the minimum.

 

[kbp911]

Your right I meant CC was .2 sorry about that.
I just tested it and it went from yesterdays 5.4 to 1.8 in a matter of 24 hrs. Yes we had very bright direct sunlight today but that is too much of a loss especially with the CYA at 60. I added addl CYA yesterday also so that number should be around 80 soon. I will try to SLAM it and see what happens. Thanks again!

 

[UN1017]

I take it you also stating that I did not need to add the calcium due to it being an vinyl liner?

Correct. Low CH levels are typically only a concern with plaster and some fiberglass pools.

I ran the SWG at 70% for the last 12 hrs last night so if I get another zero reading then the T15 must be bad.

At that time and percentage, you would only get about a 2 ppm increase which would easily get eaten up by anything growing in the water. Don't count your SWG out yet unless you are getting errors or other indications it's bad. I would turn off your SWG, successfully SLAM then turn back on your SWG and keep an eye on it. What is your typical SWG percentage and run time?

 

[kbp911]

Correct. Low CH levels are typically only a concern with plaster and some fiberglass pools.

At that time and percentage, you would only get about a 2 ppm increase which would easily get eaten up by anything growing in the water. Don't count your SWG out yet unless you are getting errors or other indications it's bad. I would turn off your SWG, successfully SLAM then turn back on your SWG and keep an eye on it. What is your typical SWG percentage and run time?

I typically run the SWG 8 hrs per day at 70 but have bumped that up to 80% for 8 hrs. I have been able to keep a steady level for the last few days between 2 to 4 ppm. I just tested it after a large rain and I am running at 2.2. I went ahead and turned it on anyway to try to get around a solid 4.

I have not looked into the details of SLAM but will do that now after I send this post.

As a side note, I was under the impression that the pool heater and was in danger if I ran the low CH. Is that also not correct?

 

[kbp911]

I am sorry for all the questions honestly but I do have one more. 1st do you use the Langelier Saturation Index or just balance the levels for each and don't worry about meeting the index. Why do some online calculators want the CYA level and some do not. I currently have a CYA level now of 70 and so far so good.

 

[UN1017]

I typically run the SWG 8 hrs per day at 70 but have bumped that up to 80% for 8 hrs. I have been able to keep a steady level for the last few days between 2 to 4 ppm. I just tested it after a large rain and I am running at 2.2. I went ahead and turned it on anyway to try to get around a solid 4.

I have not looked into the details of SLAM but will do that now after I send this post.

As a side note, I was under the impression that the pool heater and was in danger if I ran the low CH. Is that also not correct?

Remember to keep your levels in line with the Chlorine/CYA chart (below in my signature). You NEVER want your FC to fall below 3 (now 4 with your higher CYA) and you should be maintaining a FC level of 5 or 6 as much as possible. You need to bring your levels up with bleach so your SWG can maintain your target FC. The SWG can't make chorine fast enough to fix unbalanced water.

Regarding the low CH...the heater is fine. pH is what really affects corrosion on metal parts in the pool. Also, don't worry about LSI. Just use PoolMath above (uses CSI).

Here is an interesting read as well: What does Calcium Hardness really do?