Problem, 5 of my xenias are shriveld up while the other 6 are fine? 72g; plenium & refugium; 4x55w PC, 1 40w 03 NO; SG .024, NH4 0, NO2 0, NO3 0, PO4 <.5, PH 8.4 Ca 450; added iodine and trace three days ago when two were affected no change well now 5 affected; nothing has been changed or added...