Borate test strip color confusion

[atwetzel]

I think the label on my Aquachek bottle must be misprinted. The only purpleish color sample is 0 ppm, it's kind of a grayish-purple. I tested some distilled water and the test pad matched the color sample pretty closely. However, the 15 and 30 ppm color samples are both a medium light brown (I suppose) with no hint of purple that I can see. When I tested my pool, which I estmated using BleachCalc should have been at or over 32 ppm, I got a purple tinted medium light brown. Duh, now what.

What I really care about is knowing when I'm at 50 ppm, so I think I'm going to add what I calculate is needed to get there and see what color I get.

Any thoughts on how I could mix a test solution of 50 ppm to see what the test strips show? I have an accurate triple beam chemical balance that should let me weigh out as low as 1 gram. I'm not sure I remember enough of my college chemistry to fingure this out, but I'm going to try. Let's see, sodium tetraborate decahydrate is ...

[chem geek]

You need to add 1.67 grams of Sodium Tetraborate Decahydrate (10 Mule Team Borax) to 1 gallon of water to produce 50 ppm. So with your accuracy of +/- 1 gram, you could add 17 grams to 10 gallons of water and be pretty close to 50 ppm.

The trick in the calculations isn't the 381 g/mole of the Borax, but the fact that the ppm of Borates on the test strip is in ppm of Boron at 10.8 g/mole. It took Evan and I a while to figure that one out.

Richard

[atwetzel]

Thanks for figuring that borax weight per gallon value for me. I think I'll probably try figuring it out on my own to see if I can match your number. Sort of an intellectual challenge, since I took college chemstry so long ago. However, I did help my daughter with her chemistry when she was in high school a few years ago.

I should have said that my balance has a resolution of 0.1 g, or maybe 0.05 g, so that I should be able to measure in the range of 1 g reasonably well. With that in mind I weighed out 1.65-1.70 g of borax and added it to a gallon of H2O. After agitation I tested it, and to my surprise got a purple brown color that matches nothing on my AquaChek bottle. I'm guessing it's probably close to what the 15 ppm color sample should be, but maybe my strip are NG? The bottle says 2008/04 on the bottom, so they should be fresh. After several hours I agitated the solution and tested it again with the same results.

Hmmm, now I really perplexed. I think I may try getting another bottle of test strips from a different supplier. I think I also saw another brand of borate test strips at a web site somewhere.

Al

[waterbear]

LaMotte also makes a borate test strip but I have not been able to find them online....if you do please let me know! I would like to try them...Thanks!