I have had a beautiful little spathiphyllum for several years. Within the past several months, however, it has developed a strange and catastrophic problem: one by one (or several at a time, actually), the leaves have first lost their shine and tone, then turned almost black starting from the tip and/or margins. The blackness progresses slowly to the stem, then downward to the base, killing the leaf. I have some pictures, but can't figure out how to post them to this forum. In short, "plant gangrene" seems to me to be the best way to describe what's happening. It hasn't bloomed in many, many months, and the last time it did, the flowers were pretty pitiful. I know I have overwatered and/or kept it in too humid an environment in the past; I have moved it and now try to wait to water it until it starts to wilt a bit. I repotted it several weeks ago (in Miracle-Gro moisture-lock mix), but to no apparent avail--the problem continues. Old and new leaves are both vulnerable to this blackening. I don't keep it in direct sun and give it filtered water (with dilute Miracle-Gro). I don't see pests on the leaves or in the soil, so I suspect that some kind of fungus is the problem. I am very attached to this plant and will greatly appreciate any rescue suggestions.