I can't imagine the amount of antibiotic that you'll need for that particular "aquarium"!
Oh God no you don't add it to the water like you do in an aquarium! Yeah that would be some water treatment for 100,000 gallons!
But believe it or not it wouldn't take much potassium permanganate to treat a pond this size at 2 ppm. (Used to kill parasites and gram negative bacteria I believe).
Actually you either order the antibiotic premixed in with the feed, or you buy the antibiotic seperate and add it to the feed yourself. In this case you just add water and the feed at I believe 2.5 percent. Minimum order was 5 lbs. of Romet ( a broad spectrum antibiotic)so I probably have enough for the next few years if needed. That's 2.5 lbs. added per 100 lbs. of feed and I've been feeding much much less.
The trout farmer that said taking a fish to Purdue would be a waste of time basically said they would tell me I have a bacterial infection anyway so why wait for results when you can feed them a broad spectrum antibiotic? He raised brook trout and said pretty much welcome to the club. They can be a real PITA.
Interestingly today I had just enough Romet feed for one day (left over and frozen) and they fed better than they have in a long time. Go figure.
The Romet antibiotic was overnighted today so I should get it tomorrow. You only have to feed for five days straight vs. 10 days for oxytetracycline laced feed.