Difference bewteen TF100 and Store??

[sundaze]

I have a question as to why readings with the tf-1oo kit are off compared to a local store.
I had my pool installed last fall and basically closed almost immediately. The builder returns and opened the pool mid April. The water was clear over the winter. I was not home at the time but my wife said they added some chemical and asked that we bring a sample back in about two weeks.
The pool is 14000 gal fiberglass salt water filtered with sand.
Around the 1st of May I took a sample in and here were the results:
Water temp was around 58
FC 0
CC 0
TC 0
pH 8.2
TA 107
CH 170
CYA 2
Salt 3100
The builder told me to add 2 lbs of dychlor , 20 oz of muriatic acid, 5lbs of calcium increaser and when the temp came up to around 70 to add 10lbs of stabilizers, suggested filling a sock and allowing to dissolve over a couple of days.
May 10ish I purchased the TF-100 kit and tested my water….
FC 5
CC 0
TC 5
pH 7.5
TA 110
CH 375
CYA 30
Salt 3100
All of the readings I took were in the suggested range my builder’s print out . except the CYA but I was still adding….needless to say I was very happy.

Yesterday, May 17th I tessed again using the TF-100
FC 10.5
CC 0.5
TC 11.0
PH 7.7
TA 55
CH 250
CYA 65
Salt 3000
I was happy but decide since I was going by a pool store, not my builder, I would take a sample to see how my readings stacked up:
Their print out:
FC 4.7
CC 0.9
TC 5.6
pH 7.8
TA 89
CH 178
CYA 56
Salt 2900

Why the big difference in FC, TA & CH?

I went to a different store because my building is close to 75 miles away….yes this is a long way but since his reputation with fiberglass was very high we choose him over closer builders

Thanks in advanced....Dave

 

[Isaac-1]

Most likely much of it can be attributed to inaccuracy we so often see on the part of pool store testing, although this case their may be some other explanations:

FC drops over time faster with UV or heat exposure, also organic contamination will quickly consume it in a sample container. So depending on how long it took you to get to the pool store, the conditions, etc. your FC might have dropped some

TA I hate to say may be testing error on your part since it dropped considerably since your previous test only a few days before with no major chemical additions. When doing this test did you wipe the tip of the bottle of R-0009 with a damp cloth between each drop? When this reagent is very fresh (less than about a month old) it can have a static charge which can effect drop size, this is one case where too fresh can be a bad thing for testing. The good news here is you will not have to worry much about it after a couple of weeks.

For CH I am going to guess a mix of errors, your initial CH test was probably high, maybe poorly mixed water after the CH increaser addition, this is one of those tests you have to be careful going, and the swirling is important, a case where the speed stir can really come in handy. I also suspect the pool store reading being low here. Do you know if they used a drop based test or a strip based test?

So hang in there and I suspect you will soon see much more consistency with your test result, it just takes a little practice

Ike

 

[Patrick_B]

Welcome to the forum Dave.

Depending on the testing they run, you'll get varying degrees of difference on pool store/builder testing.

What we teach here, is to test properly, and trust your results. Rely on your own testing, learn what the results mean, and treat the pool accordingly.

Stores or whoever will have different results due to instrument calibration, test variation, lack of test skills, errors and on and on. As for the FC part of this, that test should be run within minutes of the sample being taken. The sooner the better, but 30 minutes at the very extreme outside for this parameter. Personally, I would never rely on a FC test sample that was 30 minutes or more old.

You will always get mixed results when comparing tests. Do your own properly, and you will have all the info you need to treat the pool.

 

[JasonLion]

It may seem counterintuitive, but pool stores have an absolutely terrible record for water testing reliability. You should just completely ignore what they said and trust your own results. The average home owner with a TF100 gets dramatically more reliable results than are available from the average pool store.

 

[zea3]

A couple of other things to remember, salt, calcium, and CYA do not evaporate out of the water. They can only be reduced by draining and refilling the pool with fresh water. Once they are added they are there until the water is drained. (There is a bacteria that consumes CYA but that only happens in very specific circumstances, usually in swamp green pools left over winter.) You can assume testing error when those results are not consistent from test to test if those chemicals have not been drained or added. You can play around with the "effects of adding chemicals" feature in PoolMath to give you an idea of what your chemical levels should be after the chemical additions you made.

Overall you should trust your own test results.

 

[sundaze]

I will always have mixed feelings about any stores because ultimately their goal is to sell me a chemical, that’s the main reason I bought the TF100. The latest store results were on a WaterLink Datamate 10 by LaMotte, whatever kind of test that is I do not know. The person took my sample and the testing was preformed out of site. I did not know that FC can change so fast. The sample was in my car for over 3 hours before testing. Also it was in a plastic bottle which I’m guessing now is not ideal. Glass I’m betting is a better choice. I should have mentioned that I am using the speed stir. The CA test I was able to repeat but I did not wipe the bottle in between drops. I did not understand why I was supposed to so I disregarded….wrong Salt, calcium and CYA I did understand can only be lowered by draining….but we had rain for a couple days before both store and my testing. Thanks for the confidence boaster

 

[duraleigh]

If pool store testing would prove itself to be precise and dependable, I doubt the TF-100 would exist.

I am a big advocate of small business but pool stores have adopted the "free testing" business plan and experience has taught us that their free testing is usually worth the time and effort they put into it............very little.

 

[Patrick_B]

I will always have mixed feelings about any stores because ultimately their goal is to sell me a chemical, that’s the main reason I bought the TF100. The latest store results were on a WaterLink Datamate 10 by LaMotte, whatever kind of test that is I do not know. The person took my sample and the testing was preformed out of site. I did not know that FC can change so fast. The sample was in my car for over 3 hours before testing. Also it was in a plastic bottle which I’m guessing now is not ideal. Glass I’m betting is a better choice. I should have mentioned that I am using the speed stir. The CA test I was able to repeat but I did not wipe the bottle in between drops. I did not understand why I was supposed to so I disregarded….wrong Salt, calcium and CYA I did understand can only be lowered by draining….but we had rain for a couple days before both store and my testing. Thanks for the confidence boaster

For the purpose of pool testing, glass or plastic does not matter at all. Three hours in your car and the FC is invalid and pH would be in question.

Rainfall will have very little effect on the test results. Even two inches would be a very small percentage of the pool content.