I think my tortoise is sick

. Recently I've found white mucus like substance in his terrarium. I don't know if this could be from the calcium supplements I give him or if there is something very seriously wrong. If you have any advice, PLEASE please please email me:
missunderstood56@hotmail.com. If I find this problem tomorrow I'll most likely take him to a vet, but there aren't any true reptile specialists where i live, so I'd rather get advice from owners and experts on here.
your help is much appreciated!
~Sara~