If you're up you may as well top it up to slam level now. You're getting closer but not quite there yet.
I suspect your additions aren't getting you to your target. Try going back to 15K. I still think your close to being done. Give it another good scrubbing like you did yesterday.
True but if your targeting 15 & only getting to 13.5 then its not dropping as much as you think at the next test. Also your testing may not be the most accurate. It shouldn't have dropped from 13.5 to 11 from 11 pm to 3 am (4 hours) then drop from 11 to 10 in the next 6 hours. Don't get stressed out over every test as you are making good progress.
I'm not sure what to say, its like the chlorine is half as strong as you think. Maybe go to Walmart & get some of their 'Pool Essentials" 10%.
PS - Is there good flow from the return lines? Should be quite strong with a 1.5 hp pump.
Whenever you go to buy liquid chlorine don't get the stock that has been sitting in the sun, as it will degrade more quickly. Also there should be a date code on the bottle that will tell you when it was made. Look up "Julian date code" on your phone and it should tell you how to read the date code on the bottle.
Wow! That's a lot! Usually a salt conversion is about break-even on cost. In your case it may payout to convert.The store I buy it from sells out every week so they are getting weekly shipments. The date code is 20183, which I believe is July 1 of this year. Sucks because they have the best price I've found for it at 5.75 a gallon