The rest of the bunch of the same plant are fine, by no means are they the Instagram condition you see in some tanks, but still good.It looks like the plant itself is struggling, and it's the only stem compared to the ones to the left and right of it (unless you see other stems that were effected). There is some new growth at the top however that looks healthy. If it's a green coating then it sounds like algae and it's taking advantage of the poor state of the plant. You may want to remove that entire stem, trim off the healthy growth, and replant those bits. What's your substrate, and are you fertilizing at all? how long is your photo period?
Perfect thank you, would you suggest trimming and then pull out the original stem and replant or will the original salvage itself?Wait until those stems develop roots, then trim and replant. In this state you could induce a full melt by trimming the plant down too much.