Stains on pool bottom

I've recently bought a house with a 10 year old in ground, 15000 gal gunite pool with a turbo-clean system. The gunite was renewed about 16 months ago by the prev owners. There are these white stains on the floor of the pool that look like someone splashed something in it while it was empty, or maybe it could be from adding shock to the water, and not brushing it up...? Am I stuck with these stains until the next time the pool is refinished, or is there a way to make them go away now? By the way, how often does gunite need refinishing?

Thanks!