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Re: Osmocote release rate

>Date: Sat, 29 Mar 1997 22:47:46 -0800
>From: "Jim Burrows" <jburrows at ix_netcom.com>
>Subject: Osmocote

> One thing I did notice is that if the balls are
>left on the surface of the gravel, you will get more algae, but used deep
>in the gravel, I noticed no increase that my SAE's and Otto's couldn't keep
>up with (IME). What I believe to be the best thing about Osmocote is the
>fact that it is a timed release fertilizer and comes in small balls that

Osmocote is a time release fertizer, but that claim is for use with
terrestrial plants. They are only exposed to water intermittently, during

While the release may be 'somewhat' controlled when completely submerged, I
suspect that it probably releases very _quickly_. I would be interested in
someone figuring out how to determine the rate of release and how long it
takes before the capsules are emptied. Or to compare an osmokote substrate
with an 'equivalent' amount of other NPK fertilizer.

While it MAY be true that you see no extra algae when it is deeply buried in
the substrate vs on the top, you might see the same with fertilizer tablets
or sticks as well. In fact, the sticks seem to have some sort of binder
which may also act as a "time releaser." I know when I put them into a glass
bottom tank to feed floating plants, they appear stay around forever. 

Just like the comments on osmokote: as long as the sticks are buried in the
substrate AND used in small quantities (e.g. less than one stick for 18" x
48" bottom, they can be used to feed the vascular plants - both thru the
roots and leaves (when small amounts leach out into the water column) -
they won't contribute to excess algae.....until you uproot a large root
plant and expose the fertilzer, that is!!
Neil Frank      Aquatic Gardeners Association         Raleigh, NC
      The Aquatic Gardener - journal of the AGA -  now in its seventh year!!