I've found a sloid fertilizer in Home Depot called Ironite (real cheap
too). It's guaranteed analysis (from the label) is as follows:

N               1%
Ca              1%
Mg              1%
S               15%
Co              0.0005%
Fe              12%
Mn              0.05%
Mo              0.0005%
Zn              1%

The nitrogen is derived from urea, and the iron is derived from pyrite and
iron sulfate, sulphur is derived from pyrites and sulphates, other elements
derived from sulphates.

Occasionally I'll chunk a pellet or two (1 to 2 mm diameter) in my 29. What
are the APD's PMDD discussions group members opinions of this fertilizer?