medium green stains in white plaster salt water pool

[gene]

Since August 20007, we have had a 16'x32' white plastered pool with an attached 7'x7' spa.

This is a salt water pool with an intellichlor chlorine generator.

Last fall I was having to clean the generator about every week or two. Then during the winter in the cold weather it shut off as it should have..

This spring the same, way to often cleaning problem reappeared.

The water has always been crystal clear and still is.
The chlorine generator has been wanting about 2 quarts of salt each day. I keep the ph balanced (it takes a quart of muriatic acid each week). I shock the pool once a week.

I bought pool time 6 way test strips and they indicated hard water and high stabilizer. I called the pool time rep and was told to add their metal stain and scale out, plus algaecide.
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June 4th (that's 7 weeks ago) I added a qt. of metal stain and scale out. The chlorine generator has not needed cleaning since then.

About 3 weeks ago streaks of a green stain ( about the color of green algae) began appearing along the two long sides of the pool and around just one pool water intake in the deep end. The streaks seem to be widening and now there is one down the middle of the pool running into the deep end, as well as on the tile at the waterline only where the spa water flows into the pool. All of these seem to be a stain as they do NOT brush off....

July 5th (3 weeks ago) I put in the recommended amount of non foaming algaecide. The stains? remain.

Not having had a plastered pool before I DON"T KNOW what it is, what to expect, or how to deal with this problem.

Whatever your help, it will be greatly appreciated.