I have Grout Efflorescence occurring in several areas of the tile wall (above the water line). It only occures on the "higher" side of the pool. The lot has a heavy slope and one wall of the pool is higher, holding back this area. It appears that ground water is leaching thru the tile/grout causing Efflorescence in several areas.
Here are a few photos, a wide and 2 close ups
I have scrubbed one of them using white vinegar, a wire brush and a stiff putty knife. With work I can get it off. I saw another post on the forum that referenced this Purity Pool OS Out Spot Stain Remover and am thinking that the muratic acid will clean more than the vinegar.