help ID'ing these nudibranches/sea slugs (?)

[Nikky.Werr]

Hello, I found these swarming my algae. Brown ones on my brown algae, green ones on my chaeto, pink/brown ones on the red algae. I guess it probably isn't a coincidence that their color matched the algae?... So I'd assume it's safe to say they eat algae, but I'm not sure. As it is, my fuge's algae has been decimated and a part of the chaeto turned white and mushy. I also found another nudibranch (?) in my DT on the glass, seemed to be eating the diatom and hair algae on the side glass but its white with thin black stripes and brown and blue spots.
The brown, green and pink/brown ones are all the same physically except for coloration, I added a picture of one of them below.
I'd like to know if I should start tearing my tank apart to find every single one if they happen to be coral eaters or if I can take it easy and simply manually remove the ones I find devouring my algae. They are rather pretty but the way they're going I'm gonna have to order more algae for my refugium and they're definitely a pest (to me anyways).

 

[Umbra]

I'd say just manually remove them as you see them. If you haven't found one on your corals but instead on your algae, chances are they're obligate algae eaters. The fact that your algae population has dropped with the appearance of these reinforces this.

 

[FishAndAquatics]

The first one is definetely a baby sea hare! It's reef safe, and gets about 6 inches and is an algae grazer. The second one looks like a berghia but much darker. Could be a zoa eating one.

 

[Nikky.Werr]

Thank you for all your input I'm keeping the first one but pulling out all the berghia looking ones as I see them.