So which test result do I believe?

[ipgregory]

Hi,

My 1st post and it's a little long, sorry. Our new pool was started just under 2 weeks ago now. It's a 15 KGal In-Ground, Plaster, Freeform.

When they came to start up the pool I was given a basic drop type test kit. The kit has no brand but tests for Total Chlorine, ph and Total Alkalinity. I used the kit for the 1st week as I started the task of balancing the water.

During a visit to the pool store to get more Chlorine later in the week I bought an AquaChek Digital Test Strip reader and some strips. It tests for Free Chlorine, ph and TA. Since these are the main tests I was concerned with right now and the startup guy had already tested my CH (250) and added stabalizer.

The Chlorine results where different of course but the ph was pretty similar. The BIG difference was the TA results. My drop kit was showing my TA rising as I was adding Baking Soda regularly. It was climbing from the initial reading of 20 and was up to 70. My target was between 100 and 120. The new test strip test showed me a TA of 140! Double the other result.

For a couple of days I tested with both kits. The Chlorine results where Ok (they where different tests, but matched what I expected), the ph was OK, they matched. The TA was always very different. My drop kit got up to 80 and then stopped. The strip test showed it climbing from 140 up to 165 as I continued to add BS per the startup guys instructions.

So I did some research on this board and others and the Taylor based reagent kits where pretty much recognized as the best. I ordered the TF-100 from here (AWSOME Service and rapid shipping by the way!).

When it arrived late this week I did a comparison test between the 3.

Un-branded drop kit (Water goes blue and has to be turned clear with counted drops) - 80
AquaChek Test Strip Reader - 190
TF-100 Kit - 110

Over the last couple of days the TF-100 result has stayed the same at 110, the other drop kit has stayed the same at 80 and the test strip has showed a gradual drop to 145. I haven't added any BS since mid week. My ph is varying little in the mid 7s. I have only added MA once this week when it climbed to 7.8. My CH is 210 and my CYA is 40. My Chlorine is up and down although I am not to concerned as the water is below 70, no bather load and I am waiting to start up my SWG in another couple of weeks. I add some every so often to keep it registering.

Should I ignore the Test Strip results and just use it for doing quick Chlorine and ph tests? Is this much variance between test kits normal? Why is my other drop kit stuck at 80? Can I rely on the TF-100, use it as my baseline test and consider my TA set for now?

Thanks

Ian

 

[waste]

Welcome to TFP!!!

I would trust the new TF 100 kit over either of the other 2!!! I know Dave (duraliegh) is meticulous about quality control! If any issue was going on with any of the tests, he'd post the info here and make good on any kits that went out with problems (there was an issue with the dropper tops earlier this year and he replaced the defective ones ) While I'm prone to trust new kits - you never know how well the pool store cared for them nor how old they are (though some do have expiration dates) nor how they were treated before they got to the pool store. Also, electronic testers need to be calibrated regularly.

I recently bought a TF 100 kit - THANKS Dave! (haven't had to use it yet ) I have put it in an attache case and it currently sits in my closet (one of the warmer places in the condo) - I'm keeping it at controlled temps and out of sunlight to protect those precious reagents. I strongly suggest that all kit owners protect their investment similarly, keep the kit at room temp and out of direct sun! (please note that the reagents that are especially susceptible to UV degradation are in UV resistant bottles - but I'd rather err on the side of caution, bad reagents = uncertain results, no matter how good your testing technique is! )

I hope Dave will see this and offer his input as well as Waterbear, chem geek and JasonLion - all those guys know the "ins and outs" of water testing a little ( ) better than I.

 

[Guest]

Even with a strip reader you are dealing with test strips and they are not called guess strips for no reason. I would trust the TF100. It is interesting that, besides the error between your cheap kit and the TF100 they gave similar results, just off by about 30 ppm. Since the precision of the TF100 is +/- 10 ppm on the TA test (and I will be generous and assume the same for your cheap kit) then it is possible that your readings are only 10 ppm off, which is not bad at all. (IF the TF100 is reading high and it's acually 100 ppm and the cheap kit is reading low and is acutally 90 ppm then you can see that your readings might not be that far apart at all.)

 

[ipgregory]

Thanks Guys for the replies. I have decided to use the TF-100 as my baseline, consider my TA to be where it needs to be or even a little high (plan to let it drop to about 90 based on some further reading of the board).

I keep it in my office on a dark shelf. The room maintains a pretty steady temperature. My startup guy suggested keeping the kit in the fridge, but I think in AZ that results in too much of a temperature swing when you get it out to use it. Even the 5 or 10 mins it is outside while you are testing means the temp of the liquids can change quite a bit.

One thing I have noticed is that there is a difference between the bottles in the cheaper kit and the TF-100. The cheaper kits bottles are stiffer in construction and have a larger, blunter nose that give a more consistent drop size. The TF-100 I have noticed can form drops that are quite different in size. This is most likely me needing to get the hang of it, but it is easier to form consistent drop sizes with the bottles in the cheaper kit and to better control the number of drops. Does anybody else have this problem? The Taylor bottles in the K-1000 kit in the TF-100 are the closest to being like the ones in the cheap kit.

With my TA set, I will monitor my ph and TC for the next couple of weeks before adding Salt and starting up my SWG. Anything special I need to watch for after I add the salt? I presume it will throw some of the other balances off to some degree and I need to be prepared to counter?

Thanks

Ian

 

[duraleigh]

Ian,

Good morning. Welcome to the forum.

I believe you are wise to keep your test kit out of the fridge. Room temp is quite a bit better, IMO, because of the rapid temp changes to the reagents which will just beg for condensation to form...particularly in the powder. Most folks test indoors.....simply go out to the pool and scoop up a cup full of pool water and bring it back in to perform your tests. (frequently at the kitchen table with a cup of coffee :-D )

If your drop size is particularly inconsistent with the T/A test, wipe the dropper tip with a damp cloth in between each drop. I know it's a PITA but Taylor recognizes that problem (as static electricity) and wiping the tip each time is the only solution available.

Your comments on the rigidity of the bottles is interesting. Some, but not all, of the bottle sizes come in three different densities. How "flexible" they are depends on...... 1. the density, 2. the bottle size, 3. the temperature. The bottles we choose are our "opinion" of what feels best but it is certainly subjective and difficult to get the perfect "feel" for everyone.

As others have said, the TF-100 (or the Taylor K-2006) has proven to be the most reliable and consistent. It does take a time or two to get used to it but Taylor chemistry has proven itself for many, many years.

 

[ipgregory]

Hi Dave,

Thanks for the reply. 1st off may I mention again your wonderful service! Shipped the same day I ordered and sitting on my doorstep when I got home 2 nights later.

I looked at the bottles again this morning when I tested and realized that all the ones in the kit had a similar 'nose' shape. The ones in my other kit are quite different. Hard to describe, but the Taylor bottles have a narrow, rounded tip. The others are Broader and flat across with a concave section inside the tip. Coupled with the stiffer bottle it is much harder to form a drop. That's a positive for me at the moment as I am still getting the hang of testing and quite often have let too many drops out by accident and had to re-do the test.

It's not a big thing and by no means majorly detracts from what is a well priced, well packaged, comprehensive and seemingly very accurate kit. I like to think though that if you don't give suppliers of products constructive feedback, they have no way of improving their product. Now improving the 'user'? Well that's a whole different problem...

I will get the hang of it and thanks very much for the kitchen table suggestion, very good idea, especially the coffee part.

Thanks

Ian

 

[MikeInTN]

Ian,
Here's a link to another thread on storage of reagents: linky.
Basically the consensus was to not refrigerate the reagents in your test kit, but rather store them at room temp somewhere nice and dark (like under a sink). I used to store my kit in my "beer" fridge in the garage, and found out that it caused my CYA readings to be off by about 20 ppm, I do believe. Luckily it caused the reading to read high rather than low, so I didn't overstabilize my pool.