there is no plant safe to put into a display tank except cheatomorpha, and it may clog your intake and cause a problem.
Suggest water changes to solve your problem: 10% a week, plus removal of all filter material, reliance on 1 lb live rock per gallon, low fish load, minimal feeding until this is solved. Bioballs, dirty filters, etc, not enough live rock and overcrowding and overfeeding are usually the cause.