Well I agree , with you Tom that P is often a limiting factor.
But using our feeding method will free up all plantnutrients accept K.
The proces consist of 2 steps that, when combinend result in lower needs of plantnutrients.
First, you slowly change from your current fishfood source to using frozen food species
with a low C - N ratio such as Mysis and Bosmina.
This will result in faster and total microbial decomposition.
So your bottem becomes cleaner and higher amounts of elements can be used by your plants.
Some high tech research is in this
http://perth.uwlax.edu/biology/aquat...rti%202002.pdf
The second step is in reducing our filtermaterial.
Biofilms in filters take up huge amouts of nitrates and TE's for there metabolism.
So we got ride of all filtermaterial and simply use them for only heating, co2 addition and water flow.
However some plants simply will not grow if there are no nitrates.
So you'll have to add a fluid-sand-filter for this purpuse.
The only element that can't be found in this fishfood is Potassium so
that's all you need to add extra.
All basic rules for a planted aquarium still have to followed.
So you will still have to add co2, plenty of light, regular
water changes and have a low KH.
Most research into this stuff has been done by leading dutch biochemist Adriaan Briene.
Before this he also studied the Redfield ratio ( N - P ratio )
His pages are in dutch but can be found here.
http://members.lycos.nl/brieneoord/a...oplankton.html
and here
http://www.xs4all.nl/~buddendo/aquar...dfield_eng.htm
Give it a try, and you'll see some amazing results.
Greetings