How to clean my tile

[zzed]

I have ceramic tile in a salt pool. No CA deposits. I'd like to clean the tiles myself just to remove dirt. Is a green sponge and baking soda ok? I do have one spot that looks like runs (coming from underneath the tile at the grout line not sure). Is it ok to use a dilute solution of muriatic acid and soft brush?

 

[sktn77a]

I'd try spraying CLR on it and scrubbing with the green scotchbrite pad first, If that doesn't work, try the muriatic acid but be careful with it - wear rubber gloves and be sure to dilute it first.