After a quick search, it seems like Endler's don't mind temperatures as high as 82, unlike guppies. My 10g doesn't go above 81 but after winter I'll probably turn it down since it gets 120F where I live and I may not even use the heater at all, depending on temperature shifts.
I didn't have a chance to test my tap but I'm fairly certain the time I tested it before, it came out 0. However, I don't think my tanks [either the 10 or the 2.5] -ever- test anything but .25 for ammonia.
I use AmQuel Plus, which detoxifies ammonia, and NovAqua so maybe it is the kit after all. I really can't remember ever seeing a 0 rating though I did see a higher rating of .5 once and about had a little heart attack. I shake every bottle and make sure to shake the second Nitrate bottle for at least thirty seconds as it says but maybe I don't shake it vigorously enough. I've come to discredit it because there's really no way my little betta all by his lonesome can make things that high. I've also never seen any healthy problems with him [until recently.. His tail is shredded but I think he might be chewing it because I don't see rot and it looks fairly U shaped and changes drastically sometimes, I've been using a mirror toy lately in the hopes of curing any boredom and the tank should be changing a lot soon].
If all else fails, I should have 2 weeks quarantine and a little less than 2 weeks in the tank to return the endlers if they don't work out? Not sure if Petsmart would take them back alive, but if they do.
The temperature is the only thing that doesn't seem to be ideal for them in my tank and I hope to get them after I get things planted so that there are plenty of places to dash around to escape my betta if he does go after them.
I've never quite understood how to add small schools of fish to an established tank though. If I'm getting 6 little Endlers, should I get them all together, quarantine, then add them all together? Or is that too much for the bioload? Should I buy, quarantine, and add three at a time until I get up to 6 total?
And would my 2.5g be far too small for a quarantine for 6 Endler's? If only for 2 weeks with twice weekly 50% water changes? The ones they have at Petsmart currently are quite young and therefore pretty small little guys. I only have the two tanks at the moment would be pretty happy about not buying another right now. I have dreams of a 20g but that's a distant dream and would rather work with what I have if I can.