Can calcium hardness disappear?

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Lykly

Lykly

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Nov 6, 2015
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Pool Size
13000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite Pro (T-15)
My fill water has a calcium hardness of ~400. It also has a TA of around 225. I filled my hot tub, and have been adding muriatic acid to lower the TA. While I've been adding the MA, I have lowered the TA to 130 but now the CH reads 25? Is this possible? I've been adding the MA until my pH gets around 7.1 and then adding when it reaches 7.8, it is dropping the TA, but I did not realize it would lower the CH like it has to this extreme. Checked it twice with my TF100 kit.

PS: I should add I also added 1800 ppm salt. I still do not understand how the CH could go from ~400 to 25


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Good job on lowering your TA, that is how it is done. No, the CH cannot drop from 400 to 25 without reverse osmosis filtration. There has to be some kind of testing error either before or after. CH can only leave the tub through splash out, overflow, leak or reverse osmosis filtration. And the only way CH could drop is if you are refilling with lower CH water.
 
That's what has me so concerned, this does not make sense. I have a new TF 100 kit, and I have done the test quite a few times over the past few years on my hot tub. Last night, I ran water from my well through my outdoor Spicket so it did not go through my water softener, and waited to get a representative sample. The reading I get from that water, is still right around that 400 ppm CH. I tested it twice. The well water over the last couple of months since I bought the house, has always been at this level, both from my testing and the pool shop. I filled the tub from the same water Spicket. I used the same test kit to check the CH in the hot tub, I also did this test twice, and the color changes upon the first drop, representing 25 ppm. Adding the MA and salt would not skew the CH test?

The reason I am so concerned about this is I will soon replaster my pool and want to use this well water to do the bicarbonate fill. But obviously if there is something crazy with my water, I would have big problems if my CH disappeared. Hoping to find out what's happening before I do that fill. I very much appreciate any help or advice with this.


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I drained the spa probably 30 days ago at my old house. I moved it to the new place, and rinsed it out prior to filling. It looked clean, and I added five ppm sanitizer, chlorine, and it has maintain that level so there's nothing eating that up. Talking to the neighbors they have never had trouble with iron, and although I know the pool store is not a good source, they show zero ppm iron. I do want to get the water tested, that a reputable place, but I still don't understand how it is disappearing. The reason I am sure it is gone is I've done multiple tests with the TF 100 kit on both the tap water from the Spicket and the hot tub. It would not bother me if there was not such a huge difference. Of course now I am in panic mode about refilling my pool when the time comes. Is there anyway that a well would produce water where the initial 20 or 30 gallons would have a high CH, and then disappear after a few hundred gallons? I wish I would have tested the hot tub water after filling prior to add any chemicals. I know when I started to fill the CH was around that 400 ppm level, but I never checked it after it was filled.


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Other than testing error...or dilution, the only way you can show loss of calcium is through scaling. If it deposited this much you would know, so i would look to testing of your spa and fill water once again. Perhaps if you refilled with softened water, that could explain it.
 
Patrick, you're possibly correct. After you said that, I realized the water I am testing from the Spicket is near the side of the house where the well water enters, the Spicket I filled the tub with, is on the opposite end of the house. I will check that tapwater, maybe that tap goes through the softener. I just came home and did this, I ran the water hose from the Spicket I have been using for 20 minutes, so I am sure at least 50 gallons probably more went through, and retested it. The calcium hardness in that water is 400, the total alkalinity is 290. I also retested my hot tub, it still shows 25 to 50 ppm. I bet you are right, I bet if I test the water out of that other Spicket it is coming softer. That would explain everything. I will check that first chance I get later this afternoon, and I will report. I'm betting you are right. Nothing else makes sense, and I am certain my testing skills are not that bad.


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Precipitation is a possible cause. However, as noted above, that should be noticeable. Some ph lock products add phosphates, which can combine with the calcium and precipitate out as calcium phosphate.

If the water was heated right away, you might have scaling in the system (plumbing, heater, filter etc.). However, that should also cause scaling on accessible surfaces as well.
 
Lykly,

There is a modified procedure for the CH test that eliminates a "vanishing endpoint". If you haven't already done so, I'd like you to try it. You start by adding a few drops of the R-0012 titrant FIRST, then the R-0010 calcium buffer followed by the R-0011L indicator dye and then finally more R-0012 drops to titrate to the endpoint. In this process, you are using the EDTA titrant drops (R-0012) initially to remove any metals that might be interfering with the test, then the R-0010 get's rid of the magnesium portion of the hardness. Finally you add the indicator dye (R-0011L) that binds with the calcium and more of the R-0012 to complete the test. You count up all the R-0012 drops you've added during the test to get the CH number.

If you are expecting 400ppm CH, then in a 25ppm/drop test (I believe that's the 10mL sample size), you would expect to have 16 drops of R-0012. Try adding 4 drops of R-0012 to the sample first, then do the rest of the test as normal.

Let us know if that works.

Matt

- - - Updated - - -

Just saw the posts about possibly adding softened water. Check that first as it is the simplest explanation.
 

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Matt I did the following prior to reading your reply, and I (I should say Patrick) think solved the mystery. It appears I have one Spicket on the outside of my house that goes through the softener. I tested the Spicket I used to fill my hot tub, and it shows 0 CH. I have a third Spicket, I tested it it shows the same as the original Spicket I used, 400 CH and 290 TA. Apparently, the one Spicket goes through the water softener, and I am certain the reason I was getting between 25 and 50 CH in the hot tub is probably because the softner could not totally keep up when I filled the hot tub. Good news is, when I go to fill my pool I will use the two Spickets that use the well water untreated. This is actually a blessing in disguise as I caught this prior to using the other Spicket, which is closest to my pool, before filling it for the bicarb fill. Thanks to everybody for the replies, I feel better now. I'm wondering, since my hot tub is fiberglass / plastic, if I need to add any hardness?


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Add CH to the tub not so much for surface protection but for foam inhibition. Low CH water tends to develop bubbles and foam easier.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006
 
Interesting that the previous owner had an external spigot plumbed to the softener. That's an unusual setup. Does the pool have an auto fill line? If not, maybe they used the softened spigot for top offs.

In any case, you might want to find a nice way to label or brass-tag that spigot so that anyone using it knows that it is softened water. You could even go to the hardware store and replace the spigot handle with a different color to make it obvious.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006
 
All I can think of is there was an outdoor kitchen added, and that Spicket might've been added at that time and tied in from the existing in-house water supply? Good idea, I think I will label it, I don't want to use it for any large water projects as it will deplete my water supply for in-house. Sure glad this was discovered prior to pool fill.


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Thanks pooldv! My TA is down to about 110 now.


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