Are slugs bad hitchikers?

[marcingo]

Hey.

So about a week ago I turned on the lights in my room and found a slug on the glass- this was at night- during the day they are nowhere to be found. Anyway its a pale sand color and has a longish body with no shell rather than a round body. I thought nothing of it and thought it might be a benefit in cleaning the glass. Yesterday I turned on the light in the early morning when it was still dark and I saw the same long one which is now about the length of half a pinky finger and a 3 or 4 more with the same color but round. I also found a black slug- again no shell but on the glass it looks the same as a turbo snail same shape mouth same spot and the body is round. Are these slugs anything to worry about? I do have quite a bit of algae on my glass that I want to get rid of so should I just leave them. It seems for 1 week they are reproducing pretty fast. Can they become harmful to corals or fish or inverts?

Thanks.