Dosing trace elements and no water changes!!.
This has to be one of the most hotly debated topics in reef keeping.
My local marine only fish store, has always told me that part C of the 'Tropic Marin' balling method adds back trace elements and magnesium. Having recently spoken to Tropic Marine, they tell me that you need to add a separate magnesium supplement. When you dose part A (calcium chloride) and part B (sodium carbonate) the chloride and the sodium get left behind, after the corals have used the carbonate and the calcium. The sodium and chloride then bond together to form common table salt (sodium chloride). This raises your salinity slightly. You remove the same amount of water from your tank, as you are dosing per week of part A.B.C, and allow the auto top off to replace pure water. This corrects the salinity. You have just removed a bit of sea water from your tank (trace elements, water and some salt), but only added salt and pure water to your tank, by adding part A+B, and some water from the auto top off (if you don't count the addition of the calcium and carbonate in part A+B). Part C simply adds trace elements to the tank, to go with the bit of salt you added from part A+B, and the pure water from the auto top off. The helps stop an imbalance of rising salt levels, or losing trace elements over time. This will not always keep up with magnesium or trace elements.
It is every reefers dream not to do water changes, and is not as difficult as you think, but not as straight forward as it sounds.
I have already made a video on how a 5% water change puts back trace elements.
I am finding that the balling salts are not keeping up with magnesium, and so have dose extra magnesium.