Glad it worked, don't believe tetracycline is typically used for ear infections but very noticeable improvement in 48 hours is usually an indication you chose one with activity against the bacteria. In a real disaster situation, with no susceptibility testing, early treatment with antibiotics might make sense as it might not only limit the contagious period of some infections but also provide information about the bacteria in question if the first ABX choice didn't help. Else the possibility exists that we wait until the infection is already becoming serious before starting a course only to find out 48-72 hours later that the ABX doesn't have activity against the bacteria, and by then a serious infection may have become life threatening.
I'm still a little leery on the powdered antibiotics however, a tainted fish product might result in a civil suit against the manufacturer but counterfeiting human drugs has got to be a felony offense. That's not to say I wouldn't use the powdered variety in a true emergency when there was no better option. The only powdered one I currently stock is
Triple Sulfa, but not intending to take it orally but use it directly on infected tissue before re-bandaging/re-packing a wound if needed.
Would just mention too that everyone should check the drug interactions and administration information for each drug you're stocking. Powdered erythromycin could be almost completely useless if it's destroyed by stomach acid (usually indicated in the administration instructions for human use as "swallow tablet whole, do not split or crush"), and tetracycline powder shouldn't be mixed with milk, or any drink mix containing calcium or magnesium, since it will bind to those minerals and
decrease its absorption. Just mention it since fish ABXs obviously won't include human administration instructions, and drugs designed for human use already take factors like extended release and absorption into account unlike ones intended for use in an aquarium.