I'm so glad I read your posts about adding chlorine this morning. I was at 5 ppm this morning and added enough "shock" to bring it up to the shock level in Watermom's chart. (If my math was right I added 8 PPM with 2 gallons of 12% chlorine) The forecast was for mostly cloudy and cool so I thought I would not lose too much over the course of the day. As often happens, it was a gorgeous sunny day and most or all of what I added is gone. Using the color chart I'm somewhere between 6 and 9 ppm as of now. I added more immediately. The good news is I can see some progress with the algae.
I should probably have mentioned that last year, we had a terrible problem with scale after "topping off" our water level in spring with hard water. Our iron filter had clogged and I had to bypass it. I thought I could deal with the consequences in the pool in time, but suddenly found myself working 90 or so hrs a week. To make a long story short, we spent most of the summer working to soften and remove it. Some of that scale is still on the liner and is giving the algae a great place to root itself.
Lastly, I wish I had found this forum before I bought a large supply of shock. Our local Ace hardware always gives a good price on larger amounts in spring so I have always loaded up. It's a good price for "shock", but still more expensive than regular bleach.
Thanks so much for the help. You can bet I'll be referring back to the forum often.