Is this an algae?

[sander]

I noticed this on 2 of my plants that I have in a 5 gallon bucket. I have a huge air stone. My ph is 6.1 and my ppm is 600. This happens to be a basil plant that is sharing a bucket with a tomato plant. I was able to flick the blob right off. I'm using white buckets and it is possible that the bucket is getting sunlight through a nearby window. None of my other plants have it.