I would start from scratch as far as the water by recycling the tank. Whatever your Neon had that wiped out your entire stock could still be in the water. your plecos are pretty hearty fish so I think it should be ok in the new tank. what type of algae eater is it? What type of fish are you putting together in the new tank? I am not sure about the dwarf frogs though. All in all, I would recycle the tank.
125 gal; New World Cichlids