There's a lot of info about using Earthworm castings on the net for aquariums.
Several of us used it here in the Bay area back a few years ago.
I think many have opted to use ADA' AS in place of it.
Some of the folks that used it well where a group of Brazilian aquarists, mostly for CO2 enriched systems, not so much the non CO2 approach , but there's no reason it will not work well there either.

If you use a sump for the HMF, then adding a sock style prefilter with a 50 micron rating will help a great deal. On a smaller system, I used a simple coffee filter that gravity feed(just like a coffee machine) and prefiltered the sponge biomedia. Kept the tank spotless and was simple to use. Coffee filters are easy and cheap to use.
Coffee and the filters are good for compost as well.

Regards,
Tom Barr