Test strip and Aqua chem 3 way checker question

[smackman]

I have used Aqua chem 3 way tester for years. I only use strips to get a reading on Alkalinity.

My Question is this: My Aqua chem liquid tester shows the bromine level to be low; My BioGuard test strips shows the total bromine to be really high..... I am confused.

My PH is 7.5; Alkalinity shows to be approx 120 - 150 ppm on test strips; We run the Hot tub a 103 degrees and use it 4-5 days a week. The water is 30 days old but is clear.

Why am I showing the difference in Bromine levels between the test strip and Aqua Chem 3 way checker?

Thanks in advance.

[Hottubguy]

Because test strips aren't very reliable

[smackman]

Because test strips aren't very reliable

Is there a possible "chemistry reason" for this huge discrepancy?

[Spoiledrotten]

I bought one of the AquaChek meters recently after reading many good and bad reviews for them, but I got to thinking that if I am going to trust a strip where all I can do is guess at what chemical level the water is by my guess at the shade of the strip, I may as well trust something that will test the color for me and then give me a digital reading to go by.

About the most helpful and common sense tip I read was that after OR before each testing, take a Q-tip dipped in distilled water and clean the window of the meter so it will clean away any residue from the last contact with the spa/pool water. You should get a reading about as accurate as possible after doing that.

Another important step is to place the end of the strip into the window area at a 45* angle rather than laying the strip in the window and sliding it up to the stopping point. This also made sense to me.

Another reason I chose to buy the AquaChek meter is that people with health issues such as diabetes, trust this type of instrument every day with their life, so I guess I can trust it with my spa water.
 
I know that you've had a meter longer than I, so I'm not trying to preach to the choir.

But addressing your issue, I'll add that I also figured I'd use advice that I've heard health care professionals give; don't use multiple scales when you are trying to loose weight. Use one scale all the time. Different scales will most likely give you different readings. So with that, if you use different sources to measure the chemistry of your water, you'll most likely get different readings from the same sample.

[smackman]

The only reading I use test strips is to check the Alkalinity. When I change water, I adjust my chemicals and then have The pool store to check it with a water sample. I live 40 miles form the nearest Hot Tub store.



It just so happened this time I noticed the Bromine to be off the top scale on my BioGuard test strips. It had been 30 days since I had checked the Alkalinity.

[chem geek]

Test strips are difficult to be accurate for multiple reasons.  The main reason is that they depend on two physical effects for their accuracy.  One is the rate of diffusion (which depends on temperature and other factors) and the other is the size of the drop sitting on the pad when you remove them from water (which depends on the surface tension of the water).  Then for certain tests the chemistry itself can have interference from other chemicals in the water and though that can also affect drop-based tests, there is less reliable chemistry used in some of the test strips tests, especially for the Cyanuric Acid (CYA) test.

See this post for a comparison of test strip resolution, let alone accuracy.  There really is no comparison against a good drop-based test.

[Spoiledrotten]

I have got about 5 different brands of test strips, a complete brand named "drop" kit that was suggested on this site, and now, the AquaChek meter. For now, I'm going to stick with the meter. There might not be as much chemical interference with the drop test kit, but you still have to guess at the color, then on one of the test you have to do quite a bit of math after the guess work is done, to decide how much of a chem to add. Just too complicated for guess work, so it's just easier to slap a strip in the water, put it in the meter and read the results.