I imagine that the concentration of the BSFL tea varies depending on what you feed them. I don't typically add anything with a high moisture content so I don't even get the tea. In fact I often add water to make it easier for the larvae to work.
You may want to consider finding a way to harvest the prepupal (dark) larvae. I think it would be better to feed those larvae to your fish since they aren't processing any scraps at this point. I suppose they could pupate in your container, but I don't think it's the most desirable situation. All you would need to do is angle the container to about 40 degrees on an afternoon when you're at home. The final stage larvae should march right out and drop into whatever container you put underneath. If you get more than you want to use that day you can store them for several weeks at room temperature.
I hope to hear more about combining the worms and the larvae.
