Mixing anemone species can be one of your problems, though that is not always the case for all anemone owners( I have two different species of anemone in my 120g). I run carbon in my tank. Which seems to keep them from chemically attacking each other. Also, my LTA acts like it loves it when I add fresh carbon to the carbon filtration system. If you don't run carbon, I suggest you do.
Your salinity is a bit low..anemones seem to not look as good when the salinity is 1.024. shoot for 1.025 or 1.026. You can raise your salinity slowly by adding salt water to your tank when your tank needs a top off.
LTAs prefer very little current. If their oral disc is being lifted off the sand when the powerheads are on. It will make the LTA very unhappy and not want to attach. Find a place in your tank that has low flow and then dig a hole next to live rock. Place the anemone in the hole. I wouldn't try to bury its foot, because the sand will just push it out of the hole that you just made for it. If its healthy enough or has the energy. It will bury its foot and attach to the bottom of your aquarium or to the rock under the sand.
Can you show us a picture of your anemone?