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Re: Hybrid substrates

Dave Engle wrote:

"Bottom third of the substrate: 100% Profile
Middle third: 50/50 Profile/Flourite
Top third: 100% Flourite"

Dave, this should work fine. Profile has a LOT more CEC that Flourite (19.5X
more), should that be a concern - the Profile in the lower layers should be
able to snag onto any nutrient ions that migrate into the substrate and hold
them until the plant roots have a chance to absorb them.

Profile also has more Calcium (24X) and Magnesium (2.8X) than Flourite, so I
would expect that you might see an increase in GH and KH over time. Profile
also has a higher Iron concenration than Flourite (1.37X), although it is
not clear how "available" the iron in either product is without the action
of either bacteria and/or plant roots and the enzymes produced by both.

"I thought
about adding a "pinch" of peat, and/or a few Osmocote pellets on the very
bottom, but I figure those would just be more variables that might go

True...... very true..... I would be afraid of both. A Profile/Flourite
substrate bed is going to be pretty porus and I don't think that there will
be any problem for water borne nutrients to diffuse into the entire bed of
the substrate. Similarly, if you place Osmocote down there, the nutrients in
it (and I assume that your Osmocote has the same 18-6-12 ratio as the bottle
I have) are going to be able to diffuse out of the substrate and enter the
water column (of course, on the other hand, the high CEC of the Profile just
_might_ be able to hold those leaking nutrient ions down in the substrate).
If you decide to use Osmocote, use _very_ little.

I don't think peat would be a good idea, although it might offer a limited
buffer against the Ca and Mg in the Profile, preventing too high an increase
in GH and Alkalinity. My fear is that the acidic peat might cause too rapid
a release of the Iron contained in the Profile. I don't know the ionic state
of the iron, nor how tightly it is bound to the structure, but there is
certainly more than you would want released suddenly. I may be wrong on
this - Steve Pushak knows more about peat's actions than I do. But I'd say
just go with your initial recipe without any other ammendments and then use
water borne fertilizer.

James Purchase