Re: Iron and potassium

Darrell Roze writes......

>I recently read the book "Hydroponics for the Home Gardener."  It had some 
>interesting information that I have never heard about in my readings of 
>aquatic plants.
>For people using vermiculite:
>"the vermiculite you use should have as neutral a pH as possible and no 
>toxic amounts of boron or flourine." 
>Regarding trace elements:
>"Iron becomes less available to the plant as the hardness of the water 

It has been shown that chelated iron remains available in solution for
a shorter duration as calcium hardness, alkalinity, and pH increase. If
iron levels are kept constant in the solution, uptake by the plants is
greater as the pH decreases. This is one reason that I quite happy
with a pH of 6.5 while many people set their sights on neutrality.
However, this might adversely affect the availability of other nutrients.
>"Under very humid conditions, where the light level is lower, you plant will 
>require more potassium -- as much as twice the normal amount.  This is 
>because photosynthesis is more difficult with a lower light level and 
>potassium is necessary for photosynthesis."

Yes, I've read this as well.

>I know hydroponics is drastically different from an aquarium, but does 
>anyone have any thoughts on whether the above applies to aquariums?

I would expect that the above should apply. What I wonder about is the
applicability to aquatic gardening of our knowledge of the CEC of
substrates, and their ability to hold and release nutrients. The two
environments, terrestrial and submersed, seem very different.