Q.my peace lily leaf turning brown
Why are they turning brown? I changed the soil. Is that why it turn brown?
Peace lily leaves tend to turn brown when the soil is too wet, because the roots rot. When repotting, you need to use a free-draining mix; a cactus soil mixed 1/2 & 1/2 with perlite would be very good. You might want to go ahead and repot your peace lily in some new soil. Also, make sure it dries sufficiently between watering. Check the moisture well down into the pot, not just on the top. An electronic moisture meter would help. Here are a couple of articles that could help you: https://www.gardeningknowhow.com/houseplants/peace-lily/peace-lily-plants.htm
https://www.gardeningknowhow.com/plant-problems/disease/treating-root-rot-gardening-tips-for-housplants.htm