Bad news!

I may have ruined a small section of the wall of my pool (I'm not sure).

I first chipped off the encrusted (calcium?) sandpaper coating off the
stainless steel bezel as shown below:
http://www5.picturepush.com/photo/a/...40/8217918.jpg

Then I dropped it into the clear 29% muriatic acid - it immediately
bubbled and turned yellow:
http://www2.picturepush.com/photo/a/...40/8217915.jpg

Assuming therefore the sandpapery coating was calcium, I ran a 5:1 test
on a small section of wall for about 30 seconds:
http://www3.picturepush.com/photo/a/...40/8217916.jpg

The results were smooth - but - gray (and definitely not blue!
http://www4.picturepush.com/photo/a/...40/8217917.jpg

Is this what is 'supposed' to happen?