Hello; I tried treating a tank with erythromycin twice. First it was not cheap and the stuff came back after a while.
I have gotten it under control in my four tanks now (fingers crossed). One tank has been free of the stuff (Let me call it CBA) for over a year now. It was an involved process.
I was replacing the carpet in my fish tank area with the 12 in by12 in commercial vinyl tiles so I had to tear down and move my tanks anyway. I set up a tank in another area sufficient to hold my fish ( I was lucky in that I had been keeping low stock for a time.)
I cleaned each tank with a Clorox solution and the gravel as well. I also soaked all the equipment in that solution. I rinsed all well and used prime after.
I have a number of live plants and placed them in a five gallon bucket of water and dosed them and many snails with the erythromycin. Not so much cost this way. I left them in the bucket a day or two.
After that it was a matter of sitting the tanks back up in the ordinary fashion. Once filled I dosed the tanks with more prime, planted the plants and added the snails. Later added fish a few at a time.
I also set my lights on a timer so that there is just under 12 hours of light each day. I keep to a light feeding schedule and have a lot of snails.
So far so good. One tank CBA free over a year and the others either at a year or close to it.
