1. Bright, filtered sunlight or partial shade (never direct sunlight);
2. Lightly moist, well-drained soil (never wet soil);
3. Soil that is allowed to dry between watering;
4. High humidity;
5. Warmth (temperature between 65 and 80 degrees Fahrenheit (18-26 degrees Centigrade).
Here are factors that can cause decline and eventual plant death:
1. Over watering;
2. Deeply planted plants;
3. The fungal diseases Cylindrocladium spathiphylli and Phytophthora parasitica, which both cause foliar decline and root rot disease (both are encouraged by over watering and deep planting).
4. Under watering
I recommend starting fresh and repotting your plant. Start by removing your peace lily from its current pot and discard the old planting mix. Next, remove any dead or dying leaf or root tissue. Clean the planting pot in hot, soapy water and refill it with fresh potting mix (Black Gold All Purpose Potting Mix or Black Gold Natural & Organic Potting Mix are great choices). When replanting, make sure your peace lily’s upper roots are close to the surface. Then water it well and place it in a location with bright, indirect light. Allow the soil to dry quite well between watering.
I hope these recommendations help!
Happy indoor gardening,