I bought a house with pool (see sig) two weeks ago and the owner left me a mess - sticks, leaves, and green algae from a big storm the week before.
I spent the first week stumbling around using test strips that he'd left, and did at least manage to get the water clear and the strips looking right. I then took a sample to a pool store to verify and found out my CYA was 167! I've since learned here that was because the previous owner used trichlor tablets, and told me he dropped in a bag of trichlor shock once a week too.
The store's recommendation to drain down to the bottom of the skimmer then refill to the top repeatedly wasn't dropping the CYA level fast enough for me - only down to 149 after four or five repetitions - so I Google'd for a better way and found this site. What a great forum!
I quickly ordered a TF-100 kit and it showed my CYA at about 140. I drained about 75% of the water out...which I think was more than what poolcalculator.com directed, but I wanted to wind up with CYA too low rather than risk still too high...and refilled. I tested tonight afterward and here are my numbers:
The pool gets no shade all day, so I think I may end up wanting to go for 60-80ppm CYA, but for now I decided to go for 50. So, tonight I used poolcalculator.com and added 27oz by volume 100% CYA to raise it by 15ppm to 50. I checked the chart and it said a FC of 6 for CYA of 50, so I also added 7oz by volume of 78% cal-hypo that the pool store had sold me to raise the FC from 3 to 6. I'm letting the pump run on high overnight to hopefully mix everything up well.
Assuming the pH and TA are still good tomorrow morning, I'm planning to add 760oz by weight of borax and 365oz of 31.45% muriatic acid tomorrow to bring my borate from 0 to 50. Or maybe it'll be less acid, since I think the CYA I added will lower the pH some, right? I ordered the LaMotte borate test strips with my TF100 kit. Oh, I better test first to make sure there's no borate in there already.
I've read a lot of posts here and think I've got a decent handle on it, but does this all sound right? The 80ppm CH is fine for an AG vinyl pool, right?