After discussion with fellow member
smackdab, it was decided that the test should be re-written to be more clear especially in light of some of his recent data on thiosulfate reductions of chlorine (dechlorination). See HERE -
R-0007 FC drop in a sample size .
Equipment Needed
SpeedStir (is really, REALLY useful!!!)
50mL Beaker* (can be purchased on Amazon
HERE)
A 1/8th teaspoon measure (can be purchased on Amazon
HERE)
*The 50mL beaker can sit on the SpeedStir allowing easy mixing of reagents
Chemicals Needed
Taylor R-0007 - Chlorine neutralizer reagent
Taylor R-0009 - Sulfuric acid reagent
Taylor R-0010 - Sodium hydroxide calcium buffer reagent
Bromothymol Blue (BTB) - (See
Post #134 where I show two different manufacturers)
Mannitol Powder - From Amazon
HERE
Test Procedure (50mL Water Sample)***
1.) Collect a 50mL sample of pool water
2.) Add 2 drops of R-0007 to neutralize the chlorine
3.) Add enough BTB until the water turns to an easily visible blue color. The volume of BTB applied here will not affect the results of the test; it's just an indicator.
4.) Add enough R-0009 drop-wise to lower pH. You want the indicator dye to transition from blue to blue-green to yellow-green to straw yellow. Straw-yellow is the color one wants to see and it should take anywhere from 8-12 drops to get there depending on your starting pH and TA.
5.) Now add approximately 2 drops of R-0010 until the water just turns pale blue. This is the hard part - you want to get the indicator dye to just turn blue, like a baby-blue and not go all the way back to a deeper blue. Typically 2 drops is all that is needed.
6.) Add 2 level spoonfuls (1/4 teaspoon total) of Mannitol. If the water has boron in it, then the sample will turn yellow again.
7.) Add R-0010 drops until the water transitions from straw yellow to greenish-blue to baby blue, i.e., similar shade of blue from Step 5. Record how many drops of R-0010 are used in this step.
8.) Calculate ppm boron/borates by multiplying the number of drops of R-0010 used only in step 7 by 4ppm/drop in
units
***Please note - This test protocol was done using my pool water where the following was present -
FC: 6ppm
CC: 0ppm
TA: 60ppm
CYA: 90ppm
pH: 7.6
CH: 1150ppm
Borate: ~ 56ppm
Temp: 85F
Salt: 3800ppm
Alternative Test Method Volumes
For a 25mL sample, each drop of R-0010 used only in step 7 equals 7.9ppm
For a 25mL sample, you will likely only need 1 drop of the R-0007
Notes:
*Dechlorinating the sample is important. The bromothymol blue (BTB) dye is sensitive to chlorine and will be bleached by it. 2 drops of R-0007 is usually more than enough for FC in normal ranges.
*If your pool water has high levels of TA (>100 ppm), I would suggest experimenting with the the number of drops in Step 4. It is important to get the sample down below the transition point for the BTB indicator and a high TA water sample might make it necessary to use a few more drops of R-0009 (See smackdab's analysis HERE). The presence of high TA will not affect the end result.
*The amount of bromotymol blue (BTB) used in Step 3 should be adjusted to give you the best color shade you can see. The standard BTB bottles in the chemical section don't use dropper tips but are rather more like squeeze bottles. So just add enough BTB so that you can see the colors.
*The R-0010 reagent (sodium hydroxide) has a very STRONG effect on raising the pH. So it should not take much to go from pale yellow to blue in Step 5. You don't want to overshoot this and add lots of R-0010 in this step. It would be easier if the R-0010 were less concentrated but we're stuck with what we have available.
*Yes, you have to try to remember the shades of blue unfortunately. This is a titration test where you are trying to measure something called the "equivalence point", i.e., the exact pH value where there's a sharp transition from yellow to blue. This is very easily see with a pH probe (which is what you would use in a lab) but it's much harder to do with a visual color determination. So what you're really after is that exact point when the BTB changes from a greenish-blue color to baby-blue as that is the point in the pH curve where the sharpest change occurs. If anyone is interested in the chemistry details, this website has a decent explanation -
Titration Fundamentals - Chemistry LibreTexts
