I raise/house blackworms to use for my wild bettas as they prefer live food, and I prefer knowing the conditions my worms are housed in.
I just use an unheated 2 gallon tank with about an inch of gravel at the bottom. I use a small internal filter for oxygenation and throw in all my decaying Indian Almond Leaves for the blackworms to feed on.
I do a couple of water changes a week using water from my cycled tank and throw in some NLS flakes every so often. The worms can go through a surprising amount of mulm and leaves in a week.
So far fingers crossed, I have not had a single case of dropsy caused by feeding blackworms. Plus it's a guarantee I'll find my wilds' spawning after a good feed of them.