Hello Kerry,
If tha black bits are hard are almost certainly from an inline carbon filter. Eventually and if the filter has not been changed regularly, (recommendations seem to suggest once per season) some of teh carbon particals can work thier way out and into the pipe work.
The old filter needs to be removed, If it is teh Carver Crystal system, teh clera plastic cap from teh cartrige can be snapped of the old filter, and replaced in the housing to seal teh system whilst you flush the pipes out with a couple of aquarolls of fresh water to remove any remaining crystals.
replace the cartridge with a fresh one and you should be OK. a word or warning, do not try to over tighten teh new filter, as this can cause the housing to crack. The web of the filter cap should be vertical when correctly fitted.