Question on how to match color on drop test kit

[CelticDaddio]

I have a drop test kit (AquaTrends or something like that). This is probably a really dumb question but here we go.... I have been using it since last summer and I have never been able to get a decent reading on Cl or Ph. The instructions to test Cl are add five drops of yellow bottle 1, 5 drops of yellow bottle 2 then invert once to mix and then match the color to determine the FC level. When I look through the tube, from the side, the color is very pale, even after shocking 3 days straight. But the other day I happened to glance into the tube from the top and the color was very deep purple-ish, which is what I would expect from a high chlorine level. After emptying the tube, I noticed a white disc in the bottom, as if this was to be used as a background for reading the color.

My dumb question is: View the liquid/tube from the top or side to match the color on these tests?

Thanks,
Ed

[joelq]

Hi Ed - sounds like a standard drops-based chlorine test kit. You should definitely be looking from the side. The disk on the bottom is probably for another test - the test for CYA or stabilizer level (but the disk is black on my test).

[simsjim]

I find it helpful to have a white background when looking from the side, to get a better idea of the nuances of the colors. Just a thought

[shadowman]

I wish there was a more precise way of measuring these things. My Cl reading never agrees with the pool store (they are lower) and the only difference is their machine is reading the color instead of a human eyeball. I only go there for a sanity check a few times a season and to check CYA which my kit won't do. Wouldn't it be great if we could just push a button and get a printout?

[waterbear]

When I look through the tube, from the side, the color is very pale, even after shocking 3 days straight.
Ed

DPD tests will bleach out at shock levels and appear to read very low when the chlorine levels are high. This is one of their biggest drawbacks and one of the reasons I personally prefer the FAS-DPD titration test for chlorine.

[CelticDaddio]

So, it appears my kit does the DPD test, rather than the FAS-DPD?

Ed

DPD tests will bleach out at shock levels and appear to read very low when the chlorine levels are high. This is one of their biggest drawbacks and one of the reasons I personally prefer the FAS-DPD titration test for chlorine.

[waterbear]

Yes, DPD is a color matching test where you match different shades of red to a color comparator, FAS-DPD is a titiration test where you add drops until the sample turns from red to colorless.

[tenax]

+ on the idea of looking against a white background instead of the sky, etc. i accidentally did that this morning when i had the test kit sitting on a white melamine shelf and thought wow..i can really see the differences in colors now

[JJParrish]

Well, in Ben's kit he has some instructions that read:
" Note: for OTO & ph testing, use white inside label as background."

[tenax]

i'm a po' poolboy..test kit from local hardware store what instructions?