Im not sure about that mate, Im useless on the experience stakes.
The water treatment bit sounds a bit dodgy thou, Im sure you'll get responses on that. Intrestin since I was thinkin of feedin mine the occasional prawn when I get one.
But here's an idea....
What about askin your local fishmongers to sort you out with a bag of small crabs for a reasonable price and keeping them in a small tank or the sump for live feeding, as you keep them you can revert to other kinds of live food for variety? When keepin em they'll work out quite cheap I expect?
Ive got a couple of questions on this I'll be postin in a seperate thread.