Welp, the kid decided he'd be helpful and clean the glass on the tank.
Must have sprayed half the stuff into the water - all the fish were dead this morning when I went to check on the tank.
Time to start over - current residents in the tank are a few plants and 8 feeder gold fish.
Probably just going to do straight N. Pulcher this time around - but I'm going to give the tank a good cycle time as one of the brichardi died on the first day of the tank due to a .5 ppm spike in ammonia when I added the bioload.
There was one survivor, a single synodontis I found when I was emptying the tank to get it good and clean before adding the gold fish - he's since been put into an SA community tank with geophagus and will probably go back into the new tank in the future when I figure out exactly what I'll do with it.
Definitely not giving up on Tangs, though - it's pretty much down to calvus, pulcher or tropheus.