thanks for the scientific update on cause of scale.

It has been our experience that when the holding tank is by-passed, we pump plenty water and get little build-up. When overnighting in an anchorage, we just dump the tank while at sea, so have no problem pumping plenty water. This year, we are in Europe, and often in marinas for a while, so do not want to dump sewage, so pump less water.

Back to my first question. If I use the sulphuric acid, how strong a solution (the stuff in the store is 70%, that seems awfully aggressive to me) for the Lavac? How long to leave it in?

Thanks