New pool built last fall, started up and closed by pool company. Same company (that built the pool) opened it up 9 days ago and cleaned it last saturday. I didn't notice this mark until yesterday, it is in the shallow end just off the bottom step, and it looks like a 1.5" long and narrow rust stain on the floor. Tried lightly scrubbing it with the pool brush, but did nothing. My wife thought maybe a nail or screw was sittin gin there over the winter when they covered it, resulting in a rust stain. I figured I would have noticed that.

Pool is chemically balanced and filter has been running 6-8 hrs per day since opening.

Any ideas? I will wait for some responses, then contact the pool co. and have them come out and look at it.

Thanks.

 

It could be a rust stain, look for magic jack products, they have a rust stain remover that works excellent.