You say that the pool was from 1985 and you mention cracks. Has this pool every been refinished?
My pool was built in 1986. Everything was wonderful with ignorance (pucks) from then until October, 2014. I went away for three weeks packing the floater with 6 tabs. Friend was going to refill it while I was gone each week. Then the text pictures came. Was clear when I left, was turquise at week 1, was clear but furry green on sides and bottom at week 2, and when I got home it was a swap with a letter in the mailbox from code enforcement that I had to take care if it IMMEDIATELY.
This is where I screwed up. I tried to fix things and spent about $180 on "powders." With as old as my plaster was, I shouldn't have wasted a nickel on the attempt. Ultimately, in November, I drained the pool and shopped for a remodel.
Now, I'm much more educated (only a little late though). The water table is so low here in AZ that floating the pool I just don't think is possible. The pool sat empty of water until March, 2015, to save on refilling and chemicals. Shasta was slow, and I got a great price I think. For $8,900, I got a new sand filter with 3hp vs pump, new plaster 15% quartz, and 84' of new tile. They said the pool was 20,400 gallons, but I refilled the pool and the water useage was 18,000, and 1,000 to 2,000 was just my everyday amount, and the incremental increase on my bill was about $45 extra, so refilling can be a bargain.
The pool was put in service on 3/7. I hadn't yet found this site. I used 30 pucks between then and 5/15. I've since switched to bleach and my cya is currently at 50, but surprising it was up to 60, so it's come down 10. I've used about 5 gallons of acid over that time because of the new plaster.
I guess the whole point of my post is if your plaster is gross and ugly, you might just want to call it quits. Everyone was telling me that to get 28 years out of my plaster was just pure luck and that 15 years is the outer limit (but they might be wrong.)
