Clay ball substrate fertilization

I've been preparing some home-made substrate fertilizer clay balls using the
following ingredients:

Tera Stone, a natural, iron rich potter's clay (without added ingredients)
FTE - fritted trace elements (Fe,Bo,Mg,Mn etc.)
Slow-Release Fertilizer (15-15-15) - coated with a semi-permiable polymer

Flatten out a piece of the clay to about 1/4" and then sprinkle about
a tsp of FTE and a couple tsps of fertilizer onto the clay strip. Press
the granules into the clay and dab a little water on to help it stick together.
Roll it into a tube and then with a spoon, pinch off small pieces and
roll these in palm until round. Try to keep the clay balls under 1/2" dia.
since the larger balls tend to crack somewhat during drying. Repeat this
until you have several dozen clay balls and let them dry. Small cracks
may appear in the balls but I don't think this is too serious unless you
can't find coated fertilizer pellets. You can fill in the cracks with
more soft clay and even give the balls another jacket of clay. I think
you could do this by dipping the dried balls into a mixture of clay and
water (about the consistency of gravy).

I plan to use these clay balls first in a small two gallon tank which I
am setting up for Crypts. I'll be dipping the plants in a 5% bleach
solution to eliminate a bad infestation of green thread algae. Once
this small tank is stable I'll repeat the process for the 50 gal tank.
Since I've already put layers of clay and wet-screened soil into the
2 gal. I'll use clay balls in it. In the 50 gal, I'll just sprinkle
the fertilizers between the clay and soil layers. Alternatively, I
could mix the fertilizers into the lower clay layer. Any thoughts?

I thought it might be better to have the fertilizer granules in the
clay layer since I think the plant roots will tend to grow mostly
into the more permeable, soil layer. I could use water soaked vermiculite
mixed with the soil to keep it from becoming compact. The problem is
when you dislodge a plant, you tend to bring up some of the vermiculite
and soil. The soil isn't too much of a problem since it settles out
and it's not too obvious on the leaves however, the small vermiculite
flakes are a slight nuisance since they can collect on the plant
leaves and you need to brush them off. It might be interesting to
have half the tank use a soil-vermiculite mix in the middle layer
and the other half, straight soil.

Fritted trace elements are interesting. Various minerals are mixed
into glass. It doesn't have the appearance of glass but instead looks
like small grey granules. I guess the glass is kind of foamy when
it solidifies and then ground up. It looks to me like small bits of
pumice or lava rock, a kind of porous appearance. The minerals can
diffuse out very, very slowly so it is a long term supply; probably
good for years. I don't have any idea how much of the trace elements
it would supply so this is very much experimental. If this works
well, it will have the advantage that one wouldn't need daily
trace nutrient additions and very little of the trace elements would
be dissolved into the water so would mainly be available to rooted
plants, not algaes.

If you work with wet clay, you'll find that it removes a lot of
the natural oils and moisture from your skin so after you wash
your hands, you can use a bit of skin moisturizer to prevent
painful hang-nails.

Steve Pushak     in Vancouver BC    CANADA