The LG technician told me about the same. He asked me to do the tub cleaning option after every 30 washes even though I told him my area has soft water.the machine also has a self cleaning option. LG suggests to use it after every 40 washing. machine would show tcl on display i think when you have gone past that many washes without running the tub cleaning option. if your area has hard water, use descaling powder in this mode every month. if water quality is fine, still do it once every 3 months and run tub cleaner once or twice a month with just plain water (you can probably add vinegar on these cycles i think).