UV sterilizers, Mg chelation, etc.

> From: ac554 at freenet_carleton.ca (David Whittaker)
> The initial conditions of Case #1 include a UV sterilizer. That
> couldn't have helped your dissolved iron levels. In Case #2 you
> installed a carbon filter to the same effect.
	Why would you expect the UV sterilizer to affect the iron
concentrations?  I can't see any reason to expect that.  In case
2 the carbon filter was removed when the trace element addition
> one should not be afraid of overdosing with potassium and
> that one would be better off substituting KCl for K2SO4 in the PMDD.
	Why would you prefer Cl- to SO4-- in the tank?  The plants
can use sulphur in fair quantities, and I don't think they need
all that much chlorine.

> Ten days isn't long. The PMDD technique works better than what I
> had been doing. Three months will tell. I'm going to have to invest
> in nitrate and phosphate test kits. Any recommendations?
	I'm using a Wardley dry tablet test kit for nitrate, and it
seems to work well.  I ran checks on deionized water and on a test
solution of 40 ppm nitrate, and they gave good results.  I have (so
far) refused to pay $20+ for 20 phosphate tests.  I have been looking
in analytical textbooks to find a method that will function at a low
enough level.  If "Dr. Dave's" remark in Febrary that 0 - 30 ppb is
about right, then I doubt that I shall find anything suitable.
> Depends upon your chloramine levels which could be 0.5 ppm to 2.0 ppm
> or above. If you use four times the recommended dosage for chlorine
> written on the bottle, you are almost guaranteed to be alright. I have
> no idea how or if it affects micronutrients.
> and
> Paul Sears wrote...
> >Hopefully Dave W, will fill us in....
> I'm not going to get sucked into this with my very limited knowledge
> of chemistry. I'll send you the article I mentioned by a Gary Zimmerman,
> Department of Physiology, University of California. You can figure it
> out for us.
	I now have it.  Thanks.  Thiosulphate should work for chloramine
in much the same way as it does for chlorine.  A somewhat higher dosage
may be required for the same number of ppm chloramine as chlorine, 
because the former has a lower molecular weight (51.5 vs 71, so use
about 1/3 more).

> I have one question about PMDD. Will the magnesium have a tendency to
> replace the chelated micronutrients in the concentrate? Maybe it is
> better to keep it out of the mix and add it separately.
	Good question, and one I should have investigated more already.
I'll see what I can find out about the relative stabilities of the

Paul Sears   Ottawa, Canada