maybe your water is turning to wine? time to repent...
are you using any of the color enhancing foods? as their color is primarily red it makes the mulm a reddish color. plus any food that gets sucked in by the filter would give it a red color.
if not head to church:rofl::laugh:
lol too funny. are the sponges slimy with the red stuff? i had a fungus grow on my filter pads that was red and slimy. it may be that. i know that food that gets sucked up if it is red it will turn slimy red as well when it decomposes.