Iron in substrate & red leaves from strong light

> From: "A. Inniss" <andrewi at u_washington.edu>
> Are you using just CaCO3, or are you too using Dolomite?  

I was recently able to acquire powdered CaCO3 which I now use
instead of the dolomite water. It's much easier to judge the amount
of Ca in the water using this since dolomite doesn't dissolve
well and if I added a lot I'm worried it might accumulate.

> If the latter, how do you find the additional Mg affects 
> the nutrient balance for your plants?

Mg is required for plants so I don't think it is going to be a
problem. I'm using Mg & K separately as sulphates daily per
the PMDD recipe (without nitrate or micro-nutrients).

> 	If one has a laterite or similar substrate, is adding more iron
> really necessary, or could it be left out of a PMDD?

I think this depends upon what you mean by laterite. The Dupla
laterite is granules so it may not provide as much iron as a fine
clay (with about 1000 times the surface area). I'm using an iron
rich pottery clay mixed with a small amount of organic humus in
the bottom layer of my 49g. The rooted plants aren't showing any
symptoms of Fe deficiency however, the floating plants did until
I added some chelated Fe (Flourish). They responded immediately
but so did the unicellular algae. This substrate also has a middle 
layer which has a lot of earthworm castings mixed with vermiculite.
It produced a lot of ammonia and relatively high levels of phosphate
in the early weeks. I increased biological filtration and the
ammonia got converted to nitrates which hit 100 ppm. The pH has
dropped pretty low too but I'm trying to keep on top of things
with regular water changes and additions of Ca, Mg and K. Many of the 
plants initially didn't seem to like the rich substrate but are doing
much better after gaining a foot hold. The crypts are doing very
well for most of the specimens except C balansae which I had
disturbed because of cyanobacteria on it. Anyway (drifting off topic)
back to the subject. Many folks do not add any iron fertilizer
and they are primarily using a variety of soil substrates. According
to Paul, eventually the plant roots penetrate the substrate so 
thickly that the oxygen they provide raises the substrate redox
potential to the point where it is no longer producing sufficient
iron. There's just too much oxygen in the substrate at this point.
This is a dynamic equilibrium with the oxygen in the water, the
plants, light, CO2 and other nutrients providing the plants with the
essntials for photosynthesis vs. the amount of organic fuel in the
substrate and the oxygen consuming bacteria which grow there.
Don't forget about the fish. Some types tolerate low oxygen in the
water better than others.

Chelated iron additions to the water are best made in very small
doses especially if there is strong lighting and fuel for unicellular
algae. In Paul's window jars (plant, water, soil, snails and daphnia)
he adds a bit of oatmeal or catfood to stimulate bacteria which
consumes the oxygen and this increases iron availability. I think
he also makes his own Fe water using soil, water and a pinch of 

> From: "James Purchase" <jpp at inforamp_net>
James has emersed water sprite turning red under his MH lights.
> Anyone else experience this?

Yup. Red pigments in leaves are a response to strong light.
Bacopa and Hygrophila do it too.

PS. Erik, did you feel the earthquake in Seattle tonight?