A compost may be just the thing ! as the vegetation decomposes it would provide plenty of food for the worms. Leafs mixed with vegetable waste, even some old coffee grounds, will decompose and turn into a good substrate to grow worms in , only problem I see where you are is how to keep it cool ...

When i first purchased this fish ( I believe in late August last year) it was about 3 inches, starving from lack of proper sized food the shop offering only "rosey reds" almost as big as itself,not the least bit interested in any pellet food, I decided to dig some small worms to see if maybe it ...

Oh yes ! I've seen it in my two Large male Royals, right before the larger of the two relentlessly attacked and eventually killed the slightly smaller one.