Snow white growth on rocks.

Question
I have had a 90 gallon saltwater fish only aquarium for the last 7 years with very few problems.  Over the last week a snow white substance has started covering the rocks. One softball sized rock is almost completely covered now and seems to be spreading to the rest of the rockwork.  All the fish and invertebrates seem quite healthy at this time.  Can you tell me what this growth most likely is and whether it is of any real concern.

Thanks

Answer
Dennis,
Sorry for the delay in responding to your question.  I've tried to do so on several occasions and have always had trouble with the site not submitting my answer.  Very frustrating, especially because the site starts yelling at me for not responding.

At any rate, it sounds like you've got one of two things going on, but I'd like a bit more information from you so that I can give you a better answer.  Can you please describe the snow white stuff better?  For example, is it hard, soft and fluffy?  Can it easily be wiped off the rock?  Have you noticed any inverts or fish picking at it?

Thanks for your time.  I look forward to hearing back from you soon.

Regards,
Scott Johnson
Aquarium Crazy Fish
www.aquariumcrazyfish.com