NC's run a bit warm for SH (they all run right around 80*F), so you might want to consider modding it to run cooler. swapping out the stock pump for a cooler running pump (MJ's or mini jets work well). repumping the tank will drop your temp close to 3*F, which is still a bit warm, but better than nothing.
to answer your question, LR rubble and regular chemi-pure in place of the sponges are good choices. if you keep the sponges, rinse them in tankwater at least bi-weekly.