Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
a) Do Tom's suggestion of a bit less of each dose. That will slow the rise over the (long) week.
b) Yes, substitute K2SO4 instead of KNO3. I would dose perhaps half as much KNO3 each time, and make up the difference with K2SO4. While the formula is not exact, it is close enough for a straight swap of these two materials.