Question
I have had two orchids for over four months and they were doing fine until a few weeks ago. A leaf started to turn a light green then yellow at the base and eventually started to fall off. Now there's only one leaf left out of five on it. It started on one and then the other which has now lost one. Did it spread to the other one? I'm new to orchid care and don't want them to die! I even named the poor things ;-) Is there anything that I can do?

Answer
There are generally two causes.  One is an insect infestation such as scale. This might be present if you see any white fuzzy (mealy) or small helmet-like bumps (scale) on any part of the plant. The second, and most common, cause is root rot.  Either way, I recommend that you purchase a small bag of orchid potting mix.  Once you have it, unpot your plants and wash the roots thoroughly.  Remove any dead or dying roots which are "mushy".  Healthy roots are firm.  There is a good chance that you have a fair amount of root loss.  Repot each plant with its healthy roots in fresh potting mix (you may want to soak the new potting mix before use unless it is already damp).

I generally recommend to anyone that they repot newly acquired orchids.  Often these plants have not been repotted for some time or are in the wrong kind if mix for long term growing.