When I say rinsings, what I mean is tank water that's been used to clean any sort of filter media from a mature filter. Whether the media has been swished, squeezed out or whatever in the water, by the time you finish with a dirty filter, that water can be really disgusting looking. But it will have a load of BB in it, and so I pour those rinsings into a filter and that does the trick.
Might have to clean the filter a bit sooner than you would have otherwise, but it's a small price to pay for the fast cycle you get.
My cories are active most of the time but they do appear to be more active at night, like the kuhli loaches are. They do much of their hunting by night. If I watch the tank in the dark, [ no moonlights], I see the albino ones busy as can be, all over the place.