A previous post mentioned using kanuma. I highly recommend it as well. I have approximately thirty azaleas and rhododendrons in pots, and every one of them is in 100% kanuma. It ain't cheap, but it makes a huge difference. It provides the slightly acid environment that azalea roots need, and makes it virtually impossible to overwater. I have also stopped using chemical fertilizers such as Miracid, and gone to completely organic. I use pelletized, composted chicken manure [Coop Poop] on top of the soil which gradually waters in, and once a month they get a watering with a fish emulsion solution. Mine have really responded to adding the fish goop, with noticeably brighter, greener foliage. Generally speaking, you are less likely to get fertilizer burn with organic fertilizers because they dissolve gradually, rather than a flash flood of chemicals.
As an aside, check your library for a book on Satsuki azaleas by Robert Callaham. It's out of print, but an invaluable resource, really the satsuki bible. Also, when you prune, do not use a concave cutter, and do not leave a little stub. Azaleas do not callus over wounds the way other trees do. Use the orange cut paste that comes in a tube. The only toolmaker that I'm aware of that offers a convex cutter is Masakuni, and it's brutally expensive, but I know of other people who have used ordinary sidecutter pliers to get a cut that is flush to the branch.