When I had an event, I used the duramycin before the birds got to bad. Once I noticed that there was snot, and they were still fairly active and drinking. I used the tylan 50 when they aren't, or I am too slow at noticing. I ended up with birds getting sick last winter, and some it hit harder than others, and I used the aureomycin crumbles in their feed too. I used tylan 50 on the worse cases along with the aureomycin in the feed. Most the birds just the aureomycin. The FFH here in my town keeps that on the shelf pretty heavily during the winter months, not so much the summer.