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Questions about PMDD

>If I understand correctly the best method is to measure the iron content 
>of the water and dose enough PMDD to keep iron levels at .1 ppm.  I'm 
>using terralit as a substrate additive and have never had insufficient 
>iron level in my tank <.1 ppm (also no signs of iron deficiency in my 
>plants). 

I have no personal experience with Terralit, but I know it's a reputable
company.  I would hope that it is a balanced supplement which contains the
reasonable proportions of all nutrients.  It may also be like Dupla
products in that different products in their plant care line provide
different parts of the nutritional package.  If this is the case, it will
be hard to match the needs of your plants to the PMDD "recipe".  In
general, it is chancy to mix and match different brands of fertilizer
products for exactly this reason.  (I'm loosely including PMDD as a "brand"
here<g>)  You really need to know what is in each product to be able to
even guess at the effect the mix will have on your tank.

>Plant condition might be a option but I have never 
>observed an overt element deficiency in my plants.  Just slow growth in 
>some species, rising nitrate levels, and outbreaks of algae.

_MOST_ micronutrient deficiencies show up in leaf damage or abnormal
growth.  Macronutrient deficiencies are more likely to show up as straight
lack of size.  If your nitrate level is rising, I would be pretty sure your
phosphate level is as well.  The other areas to check before assuming a
micronutrient deficiency would be calcium, (although again, this more often
shows itself as abnormal growth)  magnesium and CO2.  Another possibility
is potassium, but the only potassium test kit I know of is expensive.
Since potassium is realtively safe in terms of minor overdosing, I would
just try adding a small amount, and watching for a response in the plants.
If there is no response, it's probably not a potassium deficiency.  If
there _is_ a response, you may have found your problem.

Just remember though, that by solving one nutrient deficiency, you may very
well develop another as some new nutrient becomes the limiting factor for
growth.  Erik Olson experienced this last fall, when he corrected a
nitrogen shortage just to send the tank into a calcium deficient state!<g>


Karen Randall
Aquatic Gardeners Association