Recently finished refurbishing/installing a vintage Beachport octagon spa I got free for the pickup on Craig's List (I'll relate that story elsewhere).
I'm using a 2-part bromine system (I'll be asking more questions about that elsewhere).
I often deal with things rather obsessively; I just try to channel that in ways that benefit my loved ones and me. So geeking out on water chemistry was inevitable. I also like tools and toys so multiple testing kits were also inevitable.
My first test kit was of the traditional 4-way OTO, with the 3 big bottles and 2 small bottles. Got it for 6 bucks at a liquidation store (not a great deal, but I had to start somewhere). Works fine for measuring sanitizer, pH, TA as long as you're rockin' a bromine system (and know that you need to multiply the reading by 2).
Next I picked up a Taylor Basic OTO just to get the superior (IMO) translucent comparator and the Taylor name. Was pleased to see that the dimestore and the Taylor agreed with each other.
Seldom being able to leave well enough alone, I was browsing Leslie's website and saw that they have pretty insane discounts on the Spanish language versions of their Taylor Basic OTO ($2.83), Basic DPD ($1.83), Deluxe OTO ($8.33), and Deluxe DPD ($3.83).
As far as I know, just replacing the reagents should cost more than that.
With their truly free shipping, I figured it would be worth $4.17 to play around with DPD (nice for helping chlorinated friends troubleshoot, if necessary), and I'd get the Taylor TA test along with it. Download the English instructions from Taylor's website and we're good to go, right?
All went swimmingly (sorry) except that the DPD test doesn't agree with dimestore OTO or Taylor OTO. At first I got no pinkness at all, but then decanted some spa water and MPS'ed it up to a lovely vitamin-pee yellow above 10ppm bromine according to the OTO's. At that point, the DPD finally registered about 4ppm.
And before anyone asks, yes, I know you're supposed to read the right-hand column for bromine!
TA and pH agree with dimestore and Taylor OTO.
Am I dealing with DPD reagents that have expired in a discounted-because-it-sat-in-the-warehouse-for-years test kit?
Is there something about the MPS, bromine salts, borax, anti-metal (I have rusty water), and clarifier I've dribbled into the tub that is throwing it off? I followed the Pool Calculator's recommendation for boraxing.
One other thing: I tested my tap water with the DPD and got no reading. When I've tested it in the past with OTO, I got about 2ppm. Thinkin' I might chlorinate a couple of gallons of tap water and see what happens....