hi, ive had an african tank running for about 3 months going really well, but in the last 2 weeks the bright white coral which cost me a fortune is developing brown spots, but only on the coral, not the sand or glass. the fish seem to enjoy nibbleing it but i think it looks fricking ugly, the water is crystal clear with no odour, tank is out if direct sunlight, can i stop this with an algaecide or something? i expected the coral to go a bit green but didnt expect brown spots