Measuring sodium tetraborate (borax)

[PoolDoc]

HTH 6-way has OTO testing, which is desirable for daily testing, but (as Dave notes) doesn't replace the FAS-DPD test. Also, the 6-way tests TOTAL hardness, not CALCIUM hardness. (K2006 tests calcium). And the 6-way only has enough reagent for 3 CYA tests, instead of 9 (I think) in the K2006.

[Rebecca]

I'm learning a lot... Thanks for helping me finesse.

1. Okay, I see. Here's the actual product link:
http://www.loveyourhottub.com/lamott...a-test-borate/

2. You can buy a Taylor refill for the cyanuric acid (very cheaply) and use with the HTH kit.

3. I haven't shocked the pool since going to the BBB approach. I try to run CYA at 30-40.

4. Frankly, I assumed that calcium hardness and total hardness were either the same or equivalents, since the HTH kit says the remedy for low hardness is adding calcium. Please continue my education.
Rebecca

[waterbear]

Total hardness is calcium and magnesium hardness. With plaster pools we are only interested in calcium hardness since if the calcium is too low the water can be aggresive to the plaster finish. Totql hardness is really a useless test for pools (strips only measure total hardness also.)
Also, OTO only tests total chlorine. FAS-DPD tests free and combinced chlorine, is not a color matching test but rather a drop counting test similar to the TA and Hardness tests and can directly measure chlorine levels as high as about 50 ppm with a precision of either .5 or .2 ppm.

[Rebecca]

Calcium hardness/Total hardness.

Has anyone actually experienced a situation where they had high hardness but low calcium hardness? I know its theoretically possible but I suspect it's rare. I think the principal contributor to magnesium hardness in water is dolomite. As I understand it, very large concentrations are rare on Planet Earth. In my area, dolomite is associated--in a limited distribution--with lead and zinc mining.

When I filled my pool after resurfacing, total hardness was low. I can't remember the exact number but it was less than 100. It was probably 70 because that's what our lake water tests at. I suspect that hardness is largely calcium based because of limestone formations under the lake and in watersheds. I added calcium carbonate. The water hardness increased to about 220 and has since risen to 300 without any additional calcium carbonate.

Where did the additional hardness come from? As it happens, I harvest rainwater from a roof into the pool. Apparently, ground or pulverized limestone (calcium carbonate or GCC) or dolomite (calcium magnesium carbonate) are used extensively in asphalt shingles. So it looks like I have a situation that may call for calcium hardness testing. Thanks for alerting me to this. Rebecca

[PoolDoc]

Unfortunately, Chemtura (BioGuard, AquaChem, many other brands) and especially Arch (HTH, other brands) have begun using magnesium sulfate to 'dilute' their calcium hypochlorite products. I think they may be using it elsewhere, too.

Regarding rain water -- I don't know if distilled water (rain water) could dissolve significant amounts of calcium and magnesium in the manner you imply. I'm guessing not, since roofing doesn't fail by losing all its grit. But you could check by testing the water you collect.

[Rebecca]

Good thoughts on the improbability of dissolving magnesium.

I have been completely flummoxed about actual calcium hardness in my pool. The old total hardness kit used to give me a reading of 200-250. Per your advice, I switched to the Taylor 3 bottle approach, measuring only calcium hardness. It definitely turns red after adding 20 drops of #10 and 5 drops of #llL. So there is some calcium hardness present but I am not able to discern any change in color after adding #12. At first, I thought maybe there was a very very subtle shift in color to lavender but now I've done this test a lot of times and feel very uncertain....

To make this more complicated, the old total hardness test is not showing any hardness so I assume the chemicals have gone kaput.

Thank you, Rebecca

[waterbear]

If yo had no calcium hardness present the color would not turn red when adding the indicator. It would stay blue. It just means you have not added enough titrant to reach endpoint.
My suggestion is use a 10 ml water sample, add 10 drps of calcium buffer R-0010, 3 drops of calcon indicator R-0011 and then every drop of EDTA titrant R-1012 would equal 25 ppm calcium hardness instead of 10 ppm. Therefore every 4 drops is 100 ppm so the test will go much faster, particularly when calcium levels are very high.