If you saw mites, I would recommend the treatment for that before giving a shot of Tylan. Tylan is an antibiotic and will only serve to decrease the vitamins in his system plus if he has no need of an antibiotic, it will only serve to decrease the effectiveness of the Tylan when he does have a need.
Here is something I recently saw on the internet. It says to pick a bird up and blow thru the feathers and count the number of mites seen. Then it gives this approximation of how many mites may actually be on the bird:
5 mites counted = Bird may be carrying from 100 to 300 mites
6 mites counted = Bird may be carrying from 300 to 1,000 mites (light infestation)
7 mites counted = Bird may be carrying from 1,000 to 3,000 mites - small clumps of mites seen on skin and feathers (moderate infestation)
8 mites counted = Bird may be carrying from 3,000 to 10,000 mites - accumulation of mites on skin and feathers (moderate to heavy infestation)
9 mites counted = Bird may be carrying 10,000 to 32,000 or more mites - numerous large clumps of mites seen on skin and feathers; skin pocketed with scabs (heavy infestation)
I hesitate to write this because I don't want anyone getting the wrong idea but if it helps you then it's worth it. I have never had a mite or lice problem of any kind on my place until recently. I use DE regularly and in copious amounts. Truly, until recently, I have never seen a single mite or lice on any of my birds. But about two months ago one of my Buckeye roosters began showing signs of sickness. His tail was sagging, he was low on energy, I can't remember but I think his comb may have started turning pale, and then after a couple of days I noticed that he started looking like he was wet all over. He showed no signs of any kind of CRD or anything else. I don't remember now if I gave him a shot of Tylan or not. I may have given some Denagard in the water but don't remember if I did that or not either. About a 3 days or so after I noticed he was looking wet, I went out one morning to find him dead.
Having never had a mite or lice problem, I never even thought about that. Then I noticed one of the hens starting to get that wet look too and her feathers were all matted. So I decided to bring her in the house, give her a good bath, and let her spend some time in a carrier in the house eating some applesauce Gamebird Startena mash. Well, as I was giving her a bath, I started feeling like I had things crawling on me. Then I looked down at my hands and saw they were covered in mites. Then I looked at her and saw that she was just infested with them. Then it donned on me what I had read about mites in the past with their feces matting the birds feathers and the other symptoms on lethargy and such.
So I immediately gave a dose of Ivermectin-Eprinex and then I dusted them all down good with DE. That dramatically reduced the mite population on them but it did not eliminate it. A week later I dosed them again with Eprinex and I dusted them several times with DE during the week. Still it did not eliminate the problem. So I bought some Permethrin solution at the Co-Op and sprayed it on them according to the directions as well as spraying down the whole breeding pen and area. It says to wait 2 weeks before reapplying. I've still got some time to go before reapplying but I'm gonna check them all over good on Saturday and I think I'm going to give them a bath in Adams Flea & Tick Shampoo if I see any mites on them Saturday.
I should say that I'm not exactly sure where the mites came from but it's possible I brought them home from a show I attended in December. I'd like to think that's not the case but I can't think of whatelse it may be. I've never had a problem bringing anything home from a show before. I should also say that I did get a little lax in my use of DE recently. These birds were in a breeding pen and while I've been meticulous about using DE in the coops, I never thought about using it in the breeding pens - until now.
The other thing that I think is worth noting is that none of my other birds have any signs of mites on them at all. It's really odd but the Buckeyes are the only birds that had them. I have read that like people, certain chickens will tend to attract or repel pests more than others. Perhaps Buckeyes have a special taste the mites like. I've also read that drinking a tablespoon of vinegar a day will repel mites in humans. I wonder if ACV in the water will do the same for chickens? I use ACV and will be adding some to the Buckeyes water this weekend too.
Now, having said all that, Dave is correct. All you can do is the best you can do and it sounds like you have a good handle on things. And some chickens just die.
God Bless,