Repair to Swimming Pool Concrete Slab

[jheidt2543]

I am looking for suggestions on how to repair two "blemishes" / rust spots in a residential pool slab. One adjacent to the floor drain, the other is in the middle of the pool bottom slab. It looks like they are the result of pin-holes in the concrete letting water get to the rebar. I'm attaching photos taken from above, the water is still in the pool.

On the right hand side of the first photo what looks like sand is actually residue from some sort of growth over the rust spot, it was the size of a 1/2 tennis ball and looked like a puff ball mushroom??? Anyone seen anything like this before?

The other trouble spot is next to the floor drain.

Any suggestions would be welcomed.

 

[hokie66]

If it is rust, you would have to dig it out and use normal concrete repair techniques. Could be because the reinforcement had inadequate cover. My first thought was black spot algae, which can be removed with high chlorination and a lot of elbow grease. That is probably not a floor drain, but instead a hydrostatic relief valve.