I found if one only uses kalk as there source of calcium, then magnesium levels need adjusing from time to time.
Running a co2 reactor, I found my levels always stayed around 1350ppm. Guess the dissolving media provided enough.
Also most two parts and additives like Seachems Reef Advantage Calcium, have enough magnesium to maintain levels.
FWIW, I am now using the magnesium advertised for sale on here by another aquarist. I mixed a 25g batch of Instant Ocean, following the same amounts he used in his 45g mix, but adjusted for my size and the levels for calcium and alk. were exact to what he said they would be, with no precipitate. As I dont have a new mag. kit yet, I assume those levels are exact also.
