+1, we need a photo.
Without one I can just guess. My guess would be it's not a bug but actually a small crustacean that is common to both fresh and salt water tanks. There are several species and they look like bugs but actually aren't. My second guess is that I don't know until I see a photo.
That looks a lot like a larval triops but I don't know off hand what it IS. That's a great shot and a neat find. I'm going to research it but hopefully someone else recognizes it and just pops in with an answer. Thanks for sharing. I LOVE this kind of stuff.
As a side note...it also reminds me of a hillstream loach...
When you touch it what is the texture of the body?
Most crustaceans (which these are) die when exposed to copper-based treatments. I would imagine that something that works on ich and is copper-based would work for these guys as well. That might be worth researching.