Hi, so update on this, if anyone ever finds this thread and is curious how it turned out.
The 6 that survived however just passed the 2 month mark of survivability and they are happy feeders. Even though the seller lied, he must have had them acclimated and fed, because they came very good looking.
A month before getting them I stopped cleaning all the glass, and now I have a very clean glass, they did get rid of the spot algae no problem. They are not interested in green hair algae that is currently spreading in my tank (most likely cause I put it on a longer light cycle to help develop some algae for them, but the wrong kind has developed). They also show no attention to a black beard algae that I have on anubias leaves.
They are active when the lights are on, swimming around, even sometimes chasing each other or corydoras (playfully). But the feeding. I feed blanched vegetable, bottom wafers with protein, wafers with spirulina, live mosquitos and once every three days I will drop a frozen cube of daphnia or cyclops.
They are first on every meal I throw in, they climb over corydoras, sometimes sucking on their fins to make them move away from the meal, like daphnia cube that I just fed moments ago. They will go at the cube, attach and before some fish throws them out, eat it. They are not only vegetable or algae eater by a long shot, they are fully omnivorous. This may be good news for me, cause that means they really should not go hungry.
I will give it few more months and maybe get another batch of 10, to see if I can increase their shoal.
Btw when I clean the tank ,they often latch to my hand too