The OTO test will show if you really have chlorine in your pool or not.
DPD will bleach out at high chlorine levels and give a false value of 0. If the OTO test is clear or very, very soft yellow, then the DPD is correct. However, if the OTO test is strong yellow, orange or brown, the DPD was bleached out and cannot be relied on.

The Borax will raise your pH, and add "borates" to your pool which can make the water feel softer and inhibit algae. But for now it's to get pH up into the 7's range. 20 Mule Team Borax and Arm&Hammer Washing Soda are sold in the laundry section of most supermarkets, especially here in the North East, so you can try them as well. And, of course, they sell bleach.

You need to raise your pH ASAP as vinyl liners can be damaged when pH is below 6.9, so the faster you can get it above that the better--just follow Ben's instructions. The washing soda will add to your Total Alkalinity, but let's get the pH up first--that's far more important.

Meanwhile, you can upgrade your kit to be the full equivalent of the Taylor K-2006 kit we recommend by simply purchasing the Taylor K-1515 kit through Ben's Amazon link above. It's about $20 and is the FAS-DPD test kit that can test FC up to 50 or 100 parts per million, which neither the DPD nor OTO tests can do. I have one of the Leslie's DPD units--it's merely a Taylor re-badged K-2005 kit, which we don't recommend SOLELY because it lacks the FAS-DPD test. But with the K-1515 single FAS-DPD test, you'll have the same thing and will probably never use the DPD test again!

Carl