i would rather risk the new fish dieing, then all the other ones because you didn't qt, but yeah for a few endlers id say 5 gals would be okay, just make sure you change the water alot.
Yep, both petsmart guppies died. One died the next day, out of nowhere, Then a week later I noticed the other had what I think was a kind of fungus on its side. Hours later is was dead. Petsmart sucks. They looked perfectly healthy too. I am so hoping it was nothing contagious.Be careful with guppies from petco/petsmart. In my experience they are almost always carrying disease, even if there are no outward signs. I've brought several home only to see them slowly waste away and die in the next couple of weeks, and right now I'm dealing with parasitic worms that I strongly suspect were introduced via the guppies. Don't be like me - quarantine for at least a few weeks.
Meanwhile, the endlers I bought on Aquabid are amazingly resilient.