Worries about flying bug in tank

[Pumpkincrab]

Hi guys,

I haven't been on here a while but I have noticed recently something disturbing in my tank- a few small gnat-like creatures. Not at the same time, but more of spread out. They buzz around the tank until I wave at them to the point they fly out or I squish them.
I looked and I cannot tell if they are fungus gnats, humpback gnats or fruit flies. They're so tiny, I can't tell a difference.

I know ants have the ability of digging and eating molters, but I don't think these are ants. What should I do? Need I change the substrate in case? Thank you!

[curlysister]

Most flies are harmless, they are probably attracted to food. I wouldn't change the substrate.
Can you post a picture?

[Pumpkincrab]

I'll try and get a picture the next time I see it.
Thanks Curly!