pH test with TF-100

[HouTex]

I've been testing my water with my TF-100 for well over a year. Before that I used the same Taylor pH test with the five pH levels (6.8, 7.2, 7.5, 7.8 and 8.2). I probably test for pH every other day and sometimes every day. So I've had a decent amount of practice over the last 18 months since we built the pool. I can clearly tell when the test result is 7.2 or 7.5. But anything above 7.5 is pretty much a guess. Although I've never seen the purple of 8.2, the result has gotten fairly dark red which I assume is around 8.0, but I'm not sure.

Also, I've tried to guess at 7.4 or 7.6 when the color seems slightly below or above the color of 7.5, but it's really just a guess. I don't believe I'm color blind--at least I've never had an issue before. Any ideas on distinguishing between say 7.7, 7.8, 7.9, 8.0, and 8.1?

Are they just guesses based on the shade of red you get? My problem is that above 7.5 the results all seem red to me, except some are slightly darker and some are slightly lighter. For CSI purposes there's a big difference between 7.7 and 8.1, but how can you really tell? Does 8.0 have a dark red/purple shade? Again, I don't recall ever seeing a purple tint to my test results.

This is important to me because maybe my water is leveling off at 7.8 to 7.9 and I just can't tell. Adding about 32 oz. of MA every 4-5 days is getting old.

Here are my latest test results if interested:

FC 3.5
CC 0.0
pH 7.5 (added MA yesterday morning)
TA 60
CH 510
CYA 70
Salt 3200
Borates 50
CSI -.32 at 88 degrees.

 

[harleysilo]

It bugs the heck out of me too. I wish there was a endpoint/color change drop test for PH.

 

[PSW]

If you hold a white piece of paper behind the test, it is much easier to distinguish the color (at least that's what I do ). Still isn't a perfect system, but it has helped me recently.

 

[HouTex]

Thanks. I do the white paper trick, but it still seems like various slight shades of red to me. As I just posted in an older thread on a similar topic, maybe my pH has maxed out at 7.6 and I just didn't know it. I've never seen a pink or purple shade in my test sample.

 

[JasonLion]

You can get some acid demand and/or base demand reagent and use them to change the PH of a sample so you can see the various colors.

 

[duraleigh]

I find this helpful to me...

above 8.2 purple
8.0-8.2 purplish red
7.8 pinkish red with a hint of purple
7.6 red
7.4-7.5 red with an orange cast
7.2 orange
7.0 yellow orange
6.8 and below yellow

 

[Isaac-1]

I have read that people loose their ability to distinguish shades of purple as they age, and the effect is typically measurable starting around the age of 35. I wonder if this issue many members have with the pH test may be related.

 

[Richard320]

Besides the white background, try holding the thing at arm's length. That helps me.

Also, using an extra drop tends to make the color more vivid without changing the reading. Try that, too.