will stress coat effect the fish that are already in my tank if i put stress coat in with a new fish?

I wouldn't use stress coat, the fish can survive and thrive just fine without it. I like to go as natural as possible in the water, meaning, the least amount of chemicals as possible. Only use water adjustors like pH +, pH-, water softeners, water hardeners and dechlorinator, unless of course, if a fish is actually sick, then use the proper medications. As for getting new fish, get a small 10 gallon tank for quarantine purposes, then when you get new fish in, put them in the 10 for a few days with a little bit of salt (look up salt levels online to check, but I'm pretty sure it's 1 tbsp per 5 gallons of water) and some melafix or some kind of parasite medication.

I would just acclimate into the tank. When I do a water change I do add declor and Aquarisol.

Ratt, a quarantine tank is a great idea..especially if fish are coming from a commercial petshop.

Try to look them over, as well as all the other fish in the tank, before you purchase. They should look hearty with no red spots or white/fungal spots at all.

If fish are netted properly and are healthy, their slime coat will be healthy enough to be transported.

Make sure you know if you have a fish that prefer acidic or akaline, also what temp they like. These are all things that matter to fish people, and not so much petshop people.

Peizn