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Re: Aquatic Plants Digest V3 #90

Subject: Re: Jobes sticks and PO4

>It has become clear to me that I do not understand why people are using 
>Jobes sticks.  I *thought* that the point was to place nutrients, 
>especially phosphate, into the substrate where the rooted plants could get 
>at them but the algae could not.

Yes, that is the point, although I'm in favor of keeping the PO4 as low as
possible.  That's why I like the Jobes Fern and Palm formula, which
supplies more N and K and less P.

>If the sticks are being selected for low phosphate levels and if the 
>nutrients in the sticks are going to leach into the water column anyhow, 
>why use the sticks rather than the various water additives or plain old 
>K2SO4, KNO3, etc.?

While you can't avoid _some_ transfer of substrate nutrients into the water
column. (the plants themselves move PO4 up out of the substrate and release
it through their leaves) you can limit it as much as possible.  Slow
release fertilizers are meant to release their nutrients over a period of
time.  These products are designed for terrestrial applications, and will
not slow down their release any where near as long in an environment where
they remain wet.  (we don't really know how long it takes them to release
all their nutrients when submerged)  Still,  they are easier to get down
into the substrate without flooding the water with nutrients than non-slow
release.  

Some people prefer to slow down the release of nutrients even further, by
enclosing the fertilizer in a ball of clay.  That's probably the "safest"
way of all.  I have found that I can get small pieces of the Jobes sticks
down around plant roots where I want them without causing algae problems.
I use small pieces, and let the plants tell me when they need more.
Because this product is performing the way I want it to, I haven't felt the
need to get "fancier".  as always, YMMV.  Remember that too little N & P is
a _MUCH_ less common problem than too much.

------------------------------

>Subject: Thiel Laterite
>
>Does anyone have anything experience with Thiel/AquaTech brand laterite?  I
>recently bought some at the LFS.  The instructions found on the container,
>indicate a ratio of 2oz per 25lb gravel.  This seems quite low (?).

You don't need a very large volume of laterite in the substrate for it to
be effective.

I have used Albert's laterite in the past with adequate results.  My
personal preference is still Dupla, but if cost or availability are an
issue, both Thiel/AquaTech's laterite and Karl Schoeler's Substrate Gold
work well, and are much less expensive.  

Karen Randall
Aquatic Gardeners Association