I found a strange colour in some dry rock while I was cleaning it today. Any suggestion on what it could be? It's washed off with a good scrubbing, but it's deep inside the holes so I can't get a brush in there to get it all out. I don't think it's calcium based or an algae and it doesn't smell. It's probably nothing bad, but it looks blue to me (I'm colour blind so I don't really know). If it's blue, it's probably not a natural thing in dry rock, so it's probably not wanted in the tank lol. The rock has been dry for months.


