Probably not. Where did it come from? If it was full of organics when you got it, that would be a problem. Why it isn't recommended to collect raw seawater from the beach. Properly mixed saltwater from a good mix with pure RO
water is what is recommended and what most stores would supply. What we call Red algae (or Cyanobacteria, since it really isn't a algae) is usually formed in low current areas as a result of a bit too much feeding. Happens to me now and again. It goes away, or I siphon it away if it irritates a coral.