Mold? fungus? is this safe?

i bought a rock, kinda like a live rock, but its like dead, but has little spores on it that were dried out like the rock before i put it in the aquarium. now little fluffy clearish slime foam stuff is growing on the rock, it looks like the same stuff that grows on a dead goldfish if you leave it in the tank for like 2 days after it died. im just wondering is this safe? its a 10 gal brackish tank with one green spotted pufferfish in it