Question
I recently repoted a small peace lily into a 8 " pot. Now the end 1/3 of the leaves are turning dark and dry out.

Answer
Paul,

Brown tips mean the plant is being kept too wet and you have some root rot. It needs to get nearly dry between waterings. Insert a bamboo skewer into the soil big enough to go all the way down. Cut it off a half inch above the surface of the soil. When you think it is time to water pull out the skewer and check it. If it is wet more than 1/4th of the way up it is not time to water. You don't want it totally dry but 3/4ths of it dry. This time of year we have shorter days and our plants go semi dormant. They do not use as much water so you need to cut back on the amount you give them and the frequency that you water them. When you water you also need to empty the drain tray under the plant an hour after you water. Peace Lily plants are not swamp plants. Leaving water in the trays will rot the roots. They will slowly come back.

You repotted it at the wrong time of year. All houseplants should be repotted between April 1st and July 1st when the days are getting longer, never when the days are getting shorter. In the shorter days of the year plants go semi dormant and do not use as much water. You need to reduce the amount of water you give it and the frequency. If the  pot is a lot more than 2 inches larrger than the previous pot it is too large and I recommend that you move it to a smaller more appropriate pot immediately. When you water it you need to get all the soil in the pot moist . If there are dry spots the plant will suffer also.  If you don't repot to a smaller pot now and you get all the soil in the pot moist it will never be able to use up all that water before you are coming with more water or before the roots begin to rot more. There is a good chance that if you repot you will find the plant has less roots now than it did when you repotted it a couple of months ago when you repotted it. If you find areas of soft black mushy roots you need to cut those away or they will just continue to rot even in the smaller pot. Cut the roots back to healthy wiry looking roots. Do not put any sour smelling soil  into the new smaller pot because it is full of bacteria and will cause more problems. If you need new soil mix it with perlite to create a lighter better draining soil. Use 2 parts of soil and 1 part of perlite. Water it when you are done and an hour later empty that drain tray and your tree will start growing new roots and getting healthier. Good luck.

Darlene