I dont know who reccomended tetracycline, but its a pretty useless antibiotic, except for maybe popeye or swim bladder issues.
There are two types of antibiotics, those that treat Gram + bacteria, like tetracycline, and erythomycin, and those that treat Gram - bacteria such as kanamycin, oxytetracycline, and minocycline
Most fish disease falls into the Gram - category
Most antiboitics work best mixed in food. An antiboitic that is just dumped into hard water is mostly wasted, with very little dissolving and making its way past the fishes skin. Hard calcium rich water makes this even worse.
Kanamycin is okay to put into water, for some reason it works best this way and in saltwater too.
The others should be mixed in food.
An hour away, you can always order online.
Here is a good site, you should like it.
Antibiotic Fish Flake Food
With angels, you should also consider geting the anti-protozoan flake, as they are particulary prone to this (Hole in the head) parasite/condition.
http://angelsplus.com/FlakeMedProto.htm
You have to order two anyways, and 3 oz bag is plenty big enough to last.