What's on my glass?

About 4 days after cleaning my glass, these little critters start to appear. They multiply pretty fast too - I cleaned the glass about 1 week ago and there is now about 1cm between them. They are around 1mm in length. Most are still, but some are sliding around the glass. I can't see them anywhere else in the tank - only on the glass.
Any idea what they are, and how to get rid of them if I need to?

 

They are flatworms

 

Melevsreef.com - Flatworms | How to eliminate them!

There are always many more than what you can see on the glass.

 

They look like acoel flatworms to me. They tend not to be as bad as "red planaria" flatworms described in Melev's webpage. Common acoels often crash on their own, however, you may want to treat, it's possible that they could become problematic. It's less devastating to the tank if there are fewer when you treat. Although, it's much less likely they will become problematic.
So, it's a tough call, as treatment certainly can kill off a lot of your livestock.
Increased flow and heavy skimming and siphoning is sometimes enough. Also, predators, such as some wrasse, peppermint shrimp, scooter blennies etc... will tend to keep the population under control.

 

I had them all over my glass few weeks ago. I stopped feeding my tank and they went away, 6 line will probably help too. I didn't want to try flatworm exit or any other chems to avoid poisoning my system.

 

They usually run their course.. At least they did in my tank. I had a lot of them for the first few months I had it up and running. Haven't seen any for about 3 months now though. I really wouldn't worry about them, unless its really bothering you. The 6 line will def help out though, like you mentioned.