Something called water mold (Oomycetes, phylum Oomycota) can devastate orchids. It's spread via contaminated water. It likes stagnant water. I haven't had a problem with it yet, but a few OB members have dealt with it. I clean my water storage tanks with soap every time I empty them. Oomycota include kelp, mildew, Phytophthora and diatoms.
__________________ May the bridges I've burned light my way.