IntegriTyrone

Ok, just bought a route and took over and I'm pretty new to the industry but got my CPO. I trained with the seller, who uses an old OTO kit which he keeps in the sun without a lid. During this time, I tested about half the time with his kit and it was common to get TC readings in the 1-4 range, with a few obviously 5+. When I took over recently, I started using my Taylor 2006 kit and 80% of the pools showed FC of 13+, with some in the 17-23 range. CYA off the charts, 150+ consistently, which explains the high FC. Seller doesn't test for CYA, just keeps adding TriChlor tabs and sometimes even 'shocks' or spot treats with Tri granular, has probably been doing so for years, and never talked much about draining and refilling. So, I understand how this situation came to be, but what confuses me is how these pools can test in the normal range on an OTO kit, yet have FC levels 5 times higher on FAS-DPD. Pretty sure I'm testing right: 25 ml sample, 2 scoops DPD powder, titrate R-0871 and multiply drops by 0.2, or divide drops by 5. Can any of you explain this discrepancy for me?