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Re: Substrate dosing

> Subject: Re: Substrate dosing
> I think that this method has been made way more complicated than it need be.
> I use a 20cc plastic syringe barrel (get them at the pharmacy, hack off the
> needle attachment) to inject whatever I want into the substrate. Mix up a
> liquid concentration of KNO3 or K2SO4 or CSM micromix, (or any combination)
> and fill the syringe, shove it into the substrate, and push down on the
> plunger like a neuroin addict hungry for a fix.... Well, you get the idea. I
> usually include a little red clay to pre-bind the fertilizers. I can inject
> about 100cc of concentrated "PMDD" into the substrate of a 90 gallon before
> it starts to leak back out into the water column. Algae feed off the water
> column, why dose there at all? (I do, with K2SO4, for reasons of
> convenience/insanity).
> TW

Careful, problem, you might think your dosing the substrate but you could
add it to the water column and get the same result. Folks do it all the
time, no algae.......also, what do think the flow rates through your tank's
gravel is? I think it leaks out rather fast in most cases. Diffusion alone
can account for a fair amount (liters of H20/m^2/day) of exchange. Larger
thermal differences during the 24 hrs day cycle and this will increase or if
you have cables etc.  Especially things like NO3 and K+, but NH4 is more
likely to hang out along with iron etc.

Algae feed off the water column but I have no algae, loads of nutrients in
my water column. So does this notion hold up? Are you out competing the
algae by placing PMDD in the gravel? Try this with Green water/BBA etc
sometime. See how well it works. Where is my algae? I can add PMDD to my
water column consistently, no algae. By adding the nutrients to the
substrate, what you think is happening very well may not be. It may simply
be going into the water column later.

 Agarose is on the molecular scale of a porous medium, it will will only
leak out via diffusion _very_ slowly. The rate of this leakiness can be
controlled much better. It's not something difficult to make either. Jello
is tougher:) This would allow much slower and even dosing. Roots can also
penetrate the soft gel to get at the source of nutrients.

I think if we want to pursue the idea of slow substrate dosing for real,
this gel is a good idea. Binding to clay, etc is not as consistent as the
gel, it is not as affected by pH, heat convection, proximity to the roots
and is a slower more consistent method of fertilization that cannot be
pulled up into the water column as much as a ball of fertilizer without
being trapped in the agarose gel. One would simply push the gel back into
the gravel. The rate of diffusion is slow enough as not to allow that much
in the gravel at any one time, unlike the clay balls.

Will this limit the algae? I don't think so but someone will claim so at
some point in the future, that I am sure of. It might help some and allow a
better look at this idea with a better controlled dosing. Is adding straight
doses of PMDD right into the roots helping or is possibly even hurting
them(osmotic shock/toxic levels etc)? I know at least with the gel, that
will not happen.  

Tom Barr