Since we'd done a fishless cycle & set up the biological filter to handle 5mL of ammonia a day, we were able to get quite a lot of fish all at once. We got ten neon tetras, ten black phantom tetras, & four bronze corydoras catfish. Here they are just when we got them home:
The fish seemed to settle in pretty quickly, & have even become friendly (for fish). When you stand or sit near the aquarium, most of them swim over to you. They're probably just hoping I'll feed them, but it's funny nonetheless to see them swimming over to whatever part of the tank is nearest your face.
Sadly, tragedy struck last weekend, after I did a water change & cleaned up the tank a little. One of the cories was missing. I searched the tank & hoped in vain it'd just swum into the little rock cave decoration, then I spotted a tiny corpse, floating in the plants in an eddy in the top corner of the tank.
I couldn't see anything obvious wrong with him (I assumed it was male, as it was a smaller one; the females of this species are usually larger) so he went to the compost bin. I was a little concerned that the other cories might be at risk, & the next day I discovered that another of the little catfish had a patch of white fuzzy fungus on its side. Argh!
After much googling & a question posted in the aquariums subreddit, I decided to treat the whole tank with Pimafix, a natural remedy that's supposed to help with fungus. If we don't see any improvement, I may try setting up a quarantine tank & isolating this poor fishy to treat him with something stronger. The other treatments out there are toxic to live plants. These meds also affect invertebrates, though I wouldn't be too concerned if all our 'hitchhiker snails' had a mass die-off. They're going to be a problem eventually.