We were away for just over 2 weeks over christmas, a pet minder was feeding the fish and since coming back our jewel tank has this weird brown stuff growing on the glass and heater. We cleaned the tank just before we went away. On the day we got back I scrubbed it off (its easier to get rid of than green algae), and now exactly one week later it is back. Does anyone know what it could be? If I took a photo it would just look dirty! All my levels in my tank are good, with pH now around 7, no ammonia, nitrites, nitrates etc. Fish are all well, although one was bullied badly and died a few days ago (unrelated to this I am sure, a new pair formed and they picked on this guy). Thanks.