Test Advice, TF-100

[dankirk]

Hello,

I purchased a TF-100 test kit to test my hot tub's water. I have a few questions about the testing procedures.

First, should I let the water cool before testing?

Second, when doing the FAS/DPD chlorine test, the pink water turns clear, but after sitting for a couple of minutes, it turns slight pink again. I add another drop or two and it clears again. Should I base my result on the first time it goes clear, or should I count the additional drops?

Third, when testing for TA, I add the drops to the green water, and at a point it turns a dark purplish-red. If I continue to add drops, it turns more red. Do I stop when it turns from green to purplish-red, or add until it it is a true red?

Last, is the PH test in the blue box the best PH test available? I have a difficult time determining the ph level, it doesn't seem to match any of the color gradients.

Any advice you have regarding testing the water would be helpful.

Thanks, Dan

 

[JasonLion]

The chlorine test should always be done with water straight from the spa (or pool). The CYA test isn't usually needed with a spa, but it works best with water in the 80s. The others don't matter so much, you can let the water cool if you want but it isn't required.

The FAS-DPD test will often turn pink again if you let it sit long enough. As long as it goes clear for several seconds you are done.

For the TA test (and CH) after the color starts changing, you keep adding drops as long as the color continues changing. If you add a drop and the color doesn't change any further then don't count that drop.

The PH test in the blue box is the best drop test available. You can learn to recognize the colors quite accurately with some practice. One thing that I have found to help greatly is to hold the sample up to a very bright white light source, I use the sun shining on the white painted shed, some people use a light box. Any color in the background will affect the reading and many people require a very bright light to distinguish the various shades well.

One special case for the PH test: if the FC level is very high it will turn a unique shade of red/purple that isn't on the color standard. The PH test is supposed to work up to FC of 15, though what really seems to happen is that there is a slight error around FC of 10 that increases as FC increases until somewhere around FC of 18 to 22 when the PH test stops working completely (and turns that red/purple color).

There are other ways to measure PH. The ColorQ is an electronic colorimeter that does a very good job of measuring PH and FC/CC in most situations and an alright job at the other tests but costs around $100.

 

[duraleigh]

Hi, Dan,

I don't disagree with you that the pH test is a little disconcerting at first. Jason is right...it gets easier as you do it a time or two....and there's plenty of reagent for that test.

When I first learned to test for pH, My two kids and I would hold it up to a bright white background and get a "consensus" of what we saw. It really helped all of us learn how to judge that test and, now, I don't even think about it.

I am not particularly fond of the colorQ. I considered carrying it as an alternative to the TF-100 but it just seems a little to innacurate (especially for CYA and CH) for what you pay.

 

[Guest]

One special case for the PH test: if the FC level is very high it will turn a unique shade of red/purple that isn't on the color standard. The PH test is supposed to work up to FC of 15, though what really seems to happen is that there is a slight error around FC of 10 that increases as FC increases until somewhere around FC of 18 to 22 when the PH test stops working completely (and turns that red/purple color).

There are other ways to measure PH. The ColorQ is an electronic colorimeter that does a very good job of measuring PH and FC/CC in most situations and an alright job at the other tests but costs around $100.

And the colorQ has the same interference with high sanitizer levels that the TF100 has (or any other pH test based on phenol red indicator!)
Reading the pH test gets easier with practice. Try testing your tap water and keep adding drops of yor TA titrant (sulfuric acid) one at a time to see the color change as the water become more acidic then with the same sample (which should now be a yellow color) add a drop at a time of the first reagent in the calcium test (sodium hydroxide). This will cause the pH to rise and you can see the color changes all the way trough the deep purple red color.

With enough practice you will be able to tell the pH without looking at the comparator but only at the color of the sample! It's actually one of the EASIEST color comparison type tests to read!

 

[dankirk]

Thanks for the replies. I think the test kit is great, I just want to be sure that I am using it correctly.