If you let the water/sludge mixture evaporate, you may find what you're looking for. Put the filter somewhere warm and dry - in the sun, on top of the furnace, etc. Once the liquid evaporates, scrape off what's on the the filter.
I'm on the east coast growing outdoors. It's late July, I'm looking hard for flowers/preflowers with a lupe and seeing, I don't know what. Is it too early?