TF-100 vs Pool Store using Pinpoint, why BIG diff?


Aug 20, 2009
I am sure this has been hashed about countless times, but it is bugging me now.

After having just finished a new plaster interior Memorial Day weekend, we had 14,000 gallons of water trucked in and the rest from our water company via hoses. So now I have been trying to get the chemistry under control. I purchased a TF-100 probably in late August last year so the chemicals are about 10 months old.

In looking at hardness, my testing showed a 140ppm just a couple days after the fill. I tested again the following day and I had a 150ppm reading. On that day and for the next two days I added 10lbs of CaCl for a total of 30lbs. Now I show 250ppm which I am happy with, but the pool store shows me at 350-400ppm. They use what I think is called Pinpoint. They have small plastic, foil sealed, square vials with a measured amount of powdered chemical on the bottom. They manually aspirate some of my pool water into the vial, shake, and place on a back lit device with color squares.

Similarly, I show a TA of 80, but they say 120.

And I show a high pH at or near 8.2, but they say lower - at or below 7.8.

I asked why my readings were different and he blamed my last year's chemicals. I am not sure I buy into that excuse. Am I testing things wrong? I certainly have questions about colors. The red in the TA is more like a deep pink. And how blue is blue in CH? When I see no red 'flecks' in the water after mixing, I consider this blue - but it is more of a sky blue, not like food coloring blue. I need to break out my 64 count crayola crayons to get the names for the colors. :wink:

I think my signature will show the details of my pool, but here is the summary of my readings...

FC: 0.75 (on its way back up, had a huge upswing*, then over compensated)
CC: 0
pH: 8.2 (not trusting pool store, I added 32oz of muratic acid)
TA: 80
CH: 250
CYA: <30 (not concerned with this quite yet)

*another question, does the CaCl increase my FC?




TFP Expert
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LifeTime Supporter
May 7, 2007
Silver Spring, MD
Ignore the pool store readings. Pool stores have a terrible track record at testing. There are a couple of good ones, but they are rather rare.

The TF-100 has some of the most reliable tests available, better than what most of the pools stores us. If you doubt your results, do the test again. If you are getting consistent results, your results are good.

The PH will go up rapidly during the first three to four weeks after plaster is applied, and more slowly for about a year. You need to keep the PH below 8.0, while may well mean daily acid additions during the first three or four weeks.

You should not be adding any calcium yet. As the plaster cures it will release calcium into the pool water, which could easily raise your CH level too high if you add any calcium now.

The exact colors you see in the TA and CH tests don't really matter, you are looking for something redish or bluish. The rule is to add drops till the color starts to change to something like the right color, then continue adding drops until the color doesn't change any further. The final drop, which doesn't change the color any further doesn't count.

The test reagents should last a couple of years if they are stored properly. They should be kept in a cool dark place as much as possible. After less than a year they will still be fine unless you let them freeze, get very hot for a long time, or left them in the sun for weeks.

No, calcium chloride does not increase your FC level.