I want to know what this cruddy stuff is on the top of the soil and underneath the pot. Is it mold? Something in the water? I heard that ivy plants should be kept lightly moist rather than letting the soil dry completely, is that correct? Is this plant damaged?

It's fairly common and most likely a build up of salts in the compost. I wouldn't worry about it. When was the plant last repotted?

Thanks for your reply. I bought it a little over a year ago and have never repotted it.

The white material on the soil surface appears to be bits of perlite and are not a problem. The white crusty material around the drain holes are mineral deposits that have drained from the soil. That is also normal.

If your tap water is hard, that will lead to a build-up of mineral salts in the soil. In that case, use filtered or distilled water instead. Also, fertilize very rarely if at all.

Your Pothos looks healthy and dosesn't require any significant changes in its care. You might want to consider pruning -back some of the longer stems. That will keep it more under control and also prevent older leaf loss as it ages.