Pix please. Close ups too.

I went to a local pool store and got them to test the water as well as showing them these photos. They gave me something to try, and also told me my calcium hardness was 0 -- something my PB never discussed with me. SO, I got what I need to remedy that. My other levels were ok.

1 bucket pool water (about a gal) 1 pint muratic acid. Use long rubber gloves, goggles.... Muratic is powerful stuff!
Scrub brush it, rinse well, pour any leftover into the pool around the the perimeter. Check your pH in a few hours.

Keep kids and pets away while you're working with it. We don't want to hear about any accidents.

Don't let the acid or acid water mix splash on the deck.

Calcium hardness in a fiberglass pool would be expected as there is no concrete to provide hardness. The acid.water mix will remove your buildup.

Thanks so much for your responses, poolguyNJ and repair_guy!! The cleaner the pool people gave (ok, SOLD) me has some muriatic acid in it, and it helped a lot. It is called The TilePlus Stuff. We added the calcium to the pool and I have muratic acid to dilute if I ever need to do it again. I know I have seen some bad things about Jack's products on here. The lady at the pool store told me if it was "just" calcium hardness it would have been all around the pool and not just in the areas where it looked as if mortar had run down during the frequent hard rains we've been having. I am going to use the cleaner every week or so just for maintenance.

I know this is a old old post...and maybe someone is still looking... can someone look at the attached pics and advise if this is calcium buildup????? No one has answers and the post above might be the answer...

Tile line looks like efflorescence. The white on your plaster is most likely calcium.

Treat the tile line with a solution of acid and water-about 10% acid. Scrub with a nylon brush. Lime and other soluable salts in the cement become dissolved and they expand efflorescence. It will eventually go away.

For the plaster, it's a tricky method to remove the calcium and bring out the finish. It requires dropping the pH levels to allow the acidic condition to release the calcium.

It will also bring out the plaster's attributes. The It can however make the surface a bit rough.

A separate circulating pump is required to prevent the acidic water from damaging the filter equipment. Sequestering agents must added when performing this to prevent the minerals from becoming a solid and attaching to the surface or components. The water must be re-balanced prior to allowing the filter system to be used.

If you know the brand of the plaster, you should call the manufacturer and see what they think about this method or if they have preferable way of removing the calcium.