the other day i bought plankton at a petsmart. my Jack Dempsey, parrot cichlid, and lima shovel nose love plankton but when i got home and broke open the packaging the was this brown crap in the bottom of the cubes. it was a normal cube with this brown stuff in the bottom of it. i'm not sure what it was. at first i thought it was the compounds inside the foods that separated. but my fish were very hesitant in eating it. my lima ate two pieces and coughed them up, same for my other fish. from then on i took a knife and cut the brown stuff out. my cichlids would eat a couple pieces but my lima doesn't touch it. my channel catfish and sun catfish wouldn't even eat it. whats wrong with the food? is it harmful for the fish? i also noticed some of the actual plankton pieces were brown. ill post pics if you need them for further info.