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Re: Chemists - Need Advice

> Date: Sun, 25 Oct 1998 14:12:59 EST
> From: TomWood3 at aol_com
> Subject: Chemists - Need Advice Please
> I am currently using the PMDD method with some success.  As you probably know,
> this entails dosing K2SO4 and KNO3 along with a trace element mix.  I'd like
> to experiment with additions of these and some form of phosphate in the
> substrate.

Tom, if your PMDD is successful, why change? I omitted the KNO3 and 
K2SO4 from my mix. My NO3 is about 10-15ppm and my K is about 20ppm. 
So, I as saw it, I didn't need those additions. I test my water at 
work once or twice a week, and have not noticed big changes in the 
nitrates or potassium. My phosphate is about 0.7ppm. It's a little 
high ( >0.1ppm if possible), but the algae, knock on wood, is 
non-existant. I attribute PO4 to uprooting and disturbing the fert. 
in the substrate. IMHO, I wouldn't mess with phosphates in the water, 
I think you'd be asking for trouble. I put regular house plant Jobe's 
spikes, cut up in 4 pieces, deep into the substrate around the big 
growers. Too much is a LOT worse than too little. With a good enough 
fish load, I would guess the nitrates and phosphates are within 
limits to provide good growth.
> I have a hydroponics catalogue that provides phosphate in several forms - Di-
> Ammonium Phosphate (NH4)2HPO4, Di-Potassium Phosphate K2HPO4, Mono-Ammonium
> Phosphate NH4H2PO4, Mono-Calcium Phosphate Ca(H2PO4)2+H2O, Mono-Potassium
> Phosphate KH2PO4, and Triple Superphosphate CaH4(PO4)2.
> Whew.  So, the question is - What form of the above phosphates would work well
> with K2SO4 and KNO3 and in what ratio should all three be mixed to provide an
> optimum N-P-K ratio for aquatic plants? 

As you can see, the two with Ca are going to harden your water,  
but only slightly if you you very small amounts. They also are 
going to give you real big problems if added to the water column. I 
would suggest sticking to the plant spikes for your PO4 and 
delivering it through the substrate. Try them when growth slows down 
or every few months. Not too much.  From my observations, the N-P-K 
ratio in my water column is 10ppm NO3, if possible >0.5ppm PO4, and 
20-30ppm K. All plants are happy :-). I use 2 Jobe's spikes every 3 
to 4 months, and just for the 'eaters'. Good luck.
Jamie Johnson         "Keep your eyes on the stars
Chemist-Trace Metals   and your feet on the ground"
Davis & Floyd, Inc.            -Theodore Roosevelt 
jjohnson at davisfloyd_com