Well I decided to go ahead and try the No Drain Acid Wash as described by TXFlyGuy.
Yesterday's test results.
FC 1 Been letting it get low in preparation.
CC 1 Starting to see algae.
pH 7.5 Been holding it between 7 and 7.5 to try and slowly dissolve the scale.
TA 40
CYA 20
CH 250 See note below.
Borate 5
Temp about 65
CSI calc -0.72
An aside regarding the CH value. For those of you (duraleigh in particular) who were advising me on my previous thread "Trouble Identifying Stains" I previously thought my CH was much higher. In part it has come down due to rain dilution but mostly I think it was operator error on the testing. The color change is subtle for my particular type of color blindness and I was getting some of the unusual color changes too. Getting my wife to look at the color change, and adding two drops of the third reagent before the second has given me two consistent tests less than 300 now.
Started no drain acid wash at 1am on 2/24/12.
Added 1 gallon of Leslie's "Stain and Scale 2" in lieu of the Scaletec recommended in the no drain acid wash thread. I could not find the Scaletec locally (till this morning).
Raised water level to cover most of the tiles and my usual water-line.
Added a quart of acid to get to about 7ph overnight.
Circulated for an hour.
In the morning there was no obvious improvement (maybe a little at the water line) so I went to the pool store and bought 8 gallons of acid, polyquat and found some Beautec as recommended in the no drain thread.
Added the polyquat and Beautec (64 oz) and circulated for a couple of hours. Stopped the pump and removed the timer block so it won't turn on again until I raise the pH (maybe in a couple of days).
Tried out the stainless steel brush, wow it is much harder to push around than the nylon(?) one.
pH measured 7.2
Added 8 gallons of acid, expected pH will be 4.4 from pool calc don't know how accurate that is, could not find strips that go that low and didn't look real hard.
Brushed the entire pool.
As expected the pH is <6.8. I was surprised by how the color is not so different (to my partially color blind eyes) from 6.8 if at all. I understand the advice not to let the pH fall to 6.8 cause you really don't know how low it is beyond that.
Yesterday's test results.
FC 1 Been letting it get low in preparation.
CC 1 Starting to see algae.
pH 7.5 Been holding it between 7 and 7.5 to try and slowly dissolve the scale.
TA 40
CYA 20
CH 250 See note below.
Borate 5
Temp about 65
CSI calc -0.72
An aside regarding the CH value. For those of you (duraleigh in particular) who were advising me on my previous thread "Trouble Identifying Stains" I previously thought my CH was much higher. In part it has come down due to rain dilution but mostly I think it was operator error on the testing. The color change is subtle for my particular type of color blindness and I was getting some of the unusual color changes too. Getting my wife to look at the color change, and adding two drops of the third reagent before the second has given me two consistent tests less than 300 now.
Started no drain acid wash at 1am on 2/24/12.
Added 1 gallon of Leslie's "Stain and Scale 2" in lieu of the Scaletec recommended in the no drain acid wash thread. I could not find the Scaletec locally (till this morning).
Raised water level to cover most of the tiles and my usual water-line.
Added a quart of acid to get to about 7ph overnight.
Circulated for an hour.
In the morning there was no obvious improvement (maybe a little at the water line) so I went to the pool store and bought 8 gallons of acid, polyquat and found some Beautec as recommended in the no drain thread.
Added the polyquat and Beautec (64 oz) and circulated for a couple of hours. Stopped the pump and removed the timer block so it won't turn on again until I raise the pH (maybe in a couple of days).
Tried out the stainless steel brush, wow it is much harder to push around than the nylon(?) one.
pH measured 7.2
Added 8 gallons of acid, expected pH will be 4.4 from pool calc don't know how accurate that is, could not find strips that go that low and didn't look real hard.
Brushed the entire pool.
As expected the pH is <6.8. I was surprised by how the color is not so different (to my partially color blind eyes) from 6.8 if at all. I understand the advice not to let the pH fall to 6.8 cause you really don't know how low it is beyond that.
The TA was 40 after all this. I was expecting to have to add baking soda to restore this but it is the same now as before. I can see the effects of the Borates on pH buffering. I have to add a lot more acid to bring the pH down now. I think that is good because I had to add acid quite often before to keep the pH down. 
I'll get some "after" pictures in a day or two after the water clears up and I don't have a layer of dust on the stains. It certainly seems much smoother when brushing the floor so maybe what is needed is a second treatment. I considered adding additional acid half way through on the theory that if I was using "just enough" to begin with maybe some was used up very quickly with the top layers of scale raising the pH above the effective level. It is frustrating to get so used to testing and knowing exactly what the water is doing and then flying blind down in the low pH end of things.