Yes...They will love it...Just slice it a little thin and if you have a lettuce clip stick it to the wall somewhere. OR you can weight it down with a spoon or something but it will always float up. You can drop them in boiling water for just a second and the sink better. I just use the clip and feed them to them raw. ...Make ready for epic pleco poop!!!!
You may want to do it after the room has been dark about 30 minutes. If I don't my mbuna are the only thing that eat. My plecos are too shy to eat with the others.
About 24 hours, after that it will break down and cloud your water.