Low (no) CH

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alben

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LifeTime Supporter
Apr 23, 2009
74
Central Minnesota
Here are the readings from my vinyl lined inground pool using the TF-100 test kit:
FC 13
CC 1
TC 14
pH 7.7
T/A 210
CH 0
CYA 55
Temp 64

CH is 0. It was 0 last week as well. How is this even possible? Should I be concerned? If I have to add something, what would I add? If I check my city water from the tap, I get CH 100.
 
If you filled with city water and it's 100, it should be 100 in the pool too, unless you did an RO treatment to the pool. CH is not particularly important in a liner pool.

The pH is a bit high but that could be a result of the FC level. The alk is high and adding some acid to lower it ands pointing the return eyes up is a good idea. This will also help the FC free the CC. Keep the FC up until the CC is gone or under .5 .

Did you just have a battle with algae?

Scott
 
Yeah, if your city water is 100, someone must've filled the pool with softened water. (although that's hard to imagine)

Like PGNJ said, it's not big deal in a vinyl pool and it will start to slowly climb if you refill using that tap water.
 
The last time the pool was filled with completely tap water was 8 years ago when the liner was replaced. I did the fill. I have always done the fill from a garden hose, that is directly from the city water, before the water softener.

The pool depth is 50", and I just replaced about 12" last week to lower my CYA level.

So I would have expected to have seen a rise in CH, instead of staying at 0. This is so weird.

Other odd thing, is that replacing just 12" of my water lowered my CYA from 110 down to 55. The entire time I was pumping out the water, I was pumping out from the side skimmer using a manual pool vacuum head all the while scrubbing the sides and bottom with the vacuum head. I read some place that the CYA "sticks" to the vinyl and scrubbing the vinyl while vacuuming will remove the highest concentrations of CYA. Any truth to that, or just bad info?

Also is removing water the only way to get rid of excess CYA? Does it lower any other way, such as through evaporation, sunlight, chemical breakdown, or anything else?
 
Removing CYA is done via water replacement. There is also reverse osmosis. Some reports of "mysteriously dissappearing CYA" have been linked to bacteria in the water that converts the CYA to ammonia.

I've never seen any evidence supporting the theory that CYA sticks to vinyl...

If you want to lower your TA, follow the instructions in pool school. But first, retest the TA wiping the tip of the dropper bottle in between each drop with a damp cloth. Sometimes static can build up causing irregular drops sizes skewing the results.
 
CH is not required in a vinyl liner pool, so low CH isn't a problem. Regardless of what is causing that reading, a testing error or an actually low CH level, everything will be fine.

Could you describe what you see when you add the R-0011L and mix during the CH test?
 
Knowing that having a CH of 0 is nearly an impossibility, I decided to do some more testing and experimentation.

I am using two test kits. Primarily the TF-100 and an hth 6 way from Walmart as a sort of confirmation.

Using either test kit, if I fill the vial to 25ml with pool water and add the five drops of indicator, the solution does NOT turn red, or pink. It is a very light blue from the get go. Supposed indicating 0 hardness.

So I decided to dilute the sample with distilled water. Interesting thing is that the diluted solution DOES turn pink. (Yes I verified that the distilled water alone has 0 hardness, which is expected.)

The first go around I used 5ml of pool water and filled up to the 25ml line with distilled water. So a dilution of 1:5. Using either test kit, instead of multiplying the drops by 10, I multiplied by 50. 3 drops = 150 CH.

The second go around I used 12.5ml of pool water and fill up to the 25ml line with distilled water. So a dilution of 1:2. Using either test kit, instead of multiplying the drops by 10, I multiplied by 20. 6 drops = 120 CH.

So, I am thinking, there must be some chemical in the water that is throwing off the CH test when I don't dilute the sample. By diluting the sample, I am now able to get some results.
 
This sounds like a particularly bad case of metal ion interference. Try adding a couple of drops of titrant, R-0012, to the sample before the buffer and indicator, then test as normal making sure to count the drops of titrant added initially in the total required to reach endpoint. If interference still occurs, dilute the sample one to one with distilled water, retest, and double the result.
 

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Yes, I noticed that the hth 6 way test uses only two reagents, and that the TF-100 uses 3 reagents. Is the first TF-100 reagent a neutralizer? I followed the directions of the TF-100 kit exactly. Also I did the alternate TF-100 test method of putting in two drops of the last titrant in first. Same result. Sample becomes blue, and not red/pink.

I don't think I have any metal in the water. Our city water does not have metals in it. The only metal in the pool system would be a couple of copper heat sink pipes from the pool heater. But I guess, you never know with 8 year old pool water...

So yeah, looks like I am going to have to keep doing the 1/2 dilution with distilled water. As you can see, I wound up with a CH = 120 which seems reasonable.

I have to say, this forum has been so helpful, that I have been telling other pool owners I know to check out these forums! :-D
 
If the extra drops of titrant at the start don't fix this problem, then you should contact Taylor directly (see the contact page) and tell them what you are seeing. This isn't normal, is something they should be aware of, and then let us know what they say. Either that or Dave can do this since it's a TF-100 kit, but having the actual person seeing the problem talk to the manufacturer directly is usually best.

[EDIT] I've been told that the Taylor interferences describes diluting the water as an option so apparently this is already known by Taylor. Nevertheless, it does imply that there are lots of metal ions in the water while you believe that level is low. Well, at least you've got a procedure that works now. [END-EDIT]
 
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