Ella, there's nothing to worry about.
Swimming pool chlorine is calcium hypochlorite. Short version, chlorine evaporates leaves behind calcium carbonate.
You said the pool is about 30 years old, so any pH problems with new concrete are long gone.

I would drain it, scrubing the sides as it drained, then fill it back up with new water and start over. Just in case. Might as well start out new.
But as far as anything in the concrete to worry about, nope.

Corrie

Thanks. Reading about the life span of paint, it may be time to repaint. I doubt it's been done in the last 6 years. I need to have some one who knows evaluate it. Should I paint it? If it's not painted, will the water seep out? I guess if it does need repainted, NOW is the time, before filling it with plants, right?
And if so, a dark color, right? Charcoal or black?
Ella

I don't know anything about painted pools. I can't imagine why someone would paint it though.
If it's holding water now, I would leave it alone.
Mine is concrete with a coating of Thoroseal over the concrete to make it water tight. We put black concrete dye in the Thoroseal.

Another product that you can use, which was suggested to me by a guy that puts in koi ponds, is PermaFlex.

Here is a link that might be useful: PermaFlex

I would not use Permaflex. I have known of several people in the past few years who have used it and are now in the process of peeling it back off because it is not staying water tight. It seems to develop pin holes and flakes after a few years.

If you do paint it, I'd go with black. All koi ponds are built with a black liner because the black disappears. It also look nice when the green algae starts to grow on the walls. A blue pool looks really bad with algae growing in it.

Hey Cindy! ( insert hand wavy thing here)

I'm confused about this paint thing.
I can see refinishing a swimming pool and making it look pretty.
But, if the pool is holding water and doesn't need it, why would you go to all that expense and time for a fish pond? The sides are going to get covered in algae anyway, and you won't even see it.

Corrie