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.
TIA
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.