It may be because you keep it in very filtered/low light. Just because these plants can tolerate low light conditions, it doesn't mean that they prefer them. I would move it to brighter indirect sunlight, Mine gets plenty of direct morning sunlight, and then dappled sun throughout the rest of the day.

I also refrain from using tap water. I use either rainwater that I've collected or water from my dehumidifier. You can also use distilled or RO water as well.

Does that pot have a drainage hole? If not, the roots could be in soggy, wet soil, even if the top seems only moist.

Its not technically a pot, just a plastic container but yes, it has 8 large holes in the bottom and 10 around the side where it meets the bottom. The soil looks very wet, but if I grab a handfull of it from about halfway deep, it feels damp but not damp enough to clump into a ball

I moved it out onto my covered balcony with my pothos to see if it enjoys some of the sun, it is in bright indirect light shaded by my huge pothos. I don't want it to burn, since it's not accustomed to unfiltered light

It takes a little time for plants to become acclimated to brighter light. It should do better now that it's in that bright, indirect light. Mine gets direct sunlight from morning up until around noon, but I had to give my Peace Lily time to adjust to this bright light. For the rest of the day, it gets dappled sunlight that filters down through the trees. Tho, when Summer gets here, I plan on moving it back to receive dappled sunlight for most of the day, as the sunlight becomes more intense. Since it receives this much light, I never let its soil go dry. But on the other hand, its soil never stays too soggy either. The roots still have plenty of access to fresh air, which is vital for keeping your plants happy and healthy.

Plants need access to sufficient sunlight to produce their own food. When plants are kept in low light environments, they can no longer feed themselves through photosynthesis and start to suffer. Everything you'll ever need to know about properly growing Peace Lilies can be found over on the Exotic Rainforest's website...

Caring for Spathiphyllum Species and hybrids. Growing a "Peace Lily."

It's the only source of information I go by, and my Peace Lilies have never been happier. I used to have all kinds of trouble keeping these plants alive, making all of the typical mistakes. So I stopped buying them because I got tired of unintentionally killing them. But once I finally understood how they grow in their natural habitat, properly caring for them has never been easier. :)

hey jane__ny, i thought peace lilies liked wet feet...

They like moist feet, but not wet feet.. If grown in water wet is good, obviously. But when grown in dirt moist is good. Water roots and soil roots function totally different. Any plant, no matter how tropical will suffer in soggy soil because the roots need oxygen or they'll rot. Soil roots are designed to absorb water from the soil, they won't absorb oxygen from the water in the soil. Therefore they need air pockets within the soil im order to breathe, soggy soil has no air pockets. Water roots are designed to absorb oxygen from the water, they have no need to seek out and absorb water because they have more than enough. This is true in all plants that can root in water, or soil.

Peace Lilies grow along streams and rivers where the water is constantly moving and flowing. But excess water in a pot would quickly stagnate and cut off the supply of fresh oxygen, causing the roots to suffocate and rot. Keeping the soil moist, not soggy, allows the intake of fresh air, letting your plant's roots function properly.

In the tropics lots of plants (apart from epiphytes) spend half if not more of the year in soggy waterlogged soil. However, it's the high rainfall that keeps renewing the supply of oxygenated water around the root systems. Tap water often has lots in it, although mainly water purifying chemicals, in some places fluorine, but very little if any oxygen. In the dry season water recedes and air is drawn into the soil. The plants are adapted to that sort of a cycle. And that explains why soggy from tap water isn't the same as soggy from rain water.

jane_ny, these two plants get exactly the same amount of water each time (every two, sometimes three weeks) I attend to them. The interesting thing here is that one wilted visibly more than the other - for no reason that I can advance. They are in a Public Library and it is possible that one may have benefitted from the attention of a caring patron.

But my point is that both plants have wilted down a lot more than what you see; and were well on the way to turgidity an hour later. Here is some information on the variety.