Good or bad flatworms?

[Ash1176]

From what i understand there are good and bad flatworms, the white ones will eat algae whereas the red one are the bad ones? 
What do you think about these 2?

 

 

I spotted a maybe 2-3 recently. 

[Tired]

They look like acoel flatworms. Acoels are harmless. They may appear in large numbers when the tank is young, and can stay in large numbers if the tank is overfed, but don't do any real harm. The worst they do is annoy corals by crawling on them, if there are tons. Just don't overfeed your tank a lot, and they'll eventually fade into background numbers.

[Ash1176]

Thanks @Tired, yah saw after that the bad ones have 3 tails 

[Biokitty]

This is exciting! Namely because I did not have to go through all 785 pages to find that I have harmless Acoels caused by overfeeding my tank. Would you all agree? 
about 2 mm long by 1 mm wide, flat in height 😉. Look like a white 🚀 rocket ship. 

[Tired]

Yep. Acoels don't even always indicate overfeeding, they're common in new tanks. They should fade out on their own time. If you overfeed and get tons of them, they can annoy corals a bit, but that's the worst they'll do to your tank. I have a few left over from my initial surge, and I kinda like 'em. I like to watch them glide around.