What To Clean Inside (Air-handler) AC Coils With?

What can I buy to clean the "crap" out of my air-handlers coil? I went to Home Depot today and all they had was a foam to clean the outside units coil.
Also, I was surprised to find anything in the coils. The unit is only 1 1/2 yrs old and since day one I've been using one of those filters (can't think of the name of it) that is a plastic frame, plastic grill on each side, that sandwiches two pieces of nylon mesh and a piece of foam.
I clean the filter at least every 3 wks and somehow the "crap" is still getting through the filter.
I have a small indoor dog (Cocker) and I keep his coat very short but he obviously still sheds. So I'm guessing that most of the "crap" in the coils his from him. Is there a filter I can use where nothing will get into the coils?
The reason I bought the "permanent" filter was because of the dog and I didn't want to spend $15 a month on new disposable filters. Plus the fact that I have allergies.
Also, the "crap" in the coil looks like it has turned into mold. Is that possible?
BTW, the "crap" is only on the outside part of the coil. I want get the "crap" removed before it starts working it's way into the coil.
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