Hi, Barb, welcome to the forum. Glad you joined us.
One problem you will find is that too many things work. We all have our opinions and ways that we do things. It is not a case where one way is right and everything else is wring, but more of there are so many things that work that it gets confusing knowing what to do. Some people will come across as if you don't do things their way you don't love your chicks and am abusing them, yet someone else does it totally differently and it still works great. Another factor is that we all raise chickens differently: different goals, set-ups and facilities, climate, flock make-up, management techniques, and so many other things. There is a lot of difference in someone keeping four hens in a small suburban back yard versus someone rural free ranging a lot of chickens with roosters hens, and chicks. It is usually quite difficult to do but maybe try to determine if the person answering your question has anything in common with the way you do things.
Reading between the lines I think we may be quite a bit different. I'm rural and raise dual purpose chickens for meat and eggs plus play with genetics. I use broody hens to hatch when I can but also hatch a bunch in my incubator. Still, Ill respond to your question.
I always suggest you read the label to see what the medicine actually is. In the USA it is usually (but not always) Amprolium. I don't know what is available in other countries let alone your area. But if the medicated feed you are talking about is only medicated with Amprolium, then it is not an antibiotic. It is a thiamine blocker that interferes with the reproduction of a specific protozoa that can causes Coccidiosis. It does not do anything else and may not be as bad as you think. Medicated feed does not give them immunity to Coccidiosis, it just inhibits that bugs reproduction if it is even present to start with. Still, I do not use medicated feed.
Some people use all sorts of things in water, either just for chicks when they first receive them or just forever. Some people use vinegar, you can get packets at the feed store or from certain hatcheries to add to the water (read and follow instructions carefully), some people like to add sugar to the first water new chicks drink. If you add sugar only give that the first day and clean the waterer out so the sugar does not turn sour. I don't do any of that, I just use pure water. I think it is extremely important that any water they have (whether you add anything or not) is kept fresh. I don't think adding any of that stuff to the water hurts them as long as you don't over it and it can help, especially if they are delayed in arrival and are weakened. I's use it as a treatment if I had a specific problem, not as a preventative.
I think your real question is how to raise healthy chicks. For that I try to strengthen their immune system and mainly depend on that instead of better living through drugs. I expose them to the environment they will be living in as soon as I can. My brooder is in the coop so they are exposed to the adults. I fed them dirt from the run to make sure they start working on any flock immunities they may need. I keep the brooder pretty dry, a wet brooder is a dangerous brooder. The only time I ever treat for a problem is when I have a problem to treat. Other people have totally different philosophies as I'm sure you'll quickly find out by reading on this forum. I'm sure their chickens are healthy too. It's just the way I do it.
Good luck and welcome to the adventure. It is a fun journey.
I have never fed medicated feed. I use apple cider vinegar in every other watering and once or twice a week I mix plain yoghurt and pureed home grown garden greens, a clove of garlic, (and sometimes other things, like herbs, or a cooked egg,)
