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[AGA-Member] RE: Madagascar Lace plant

shieber wrote:
> No question that lab-grade chemicals have fewer impurties than material that has not be refined as much. The question is whether that matters at all for aquatic gardening.

I doubt you will find any examples.

As hobbyists we can set aside concerns about the accuracy of the dose when using low-grade chemicals.  The purity of the chemical is a small part of the problem with accurate dosing.  The moisture in the reagent may account for as much inaccuracy as you get from other impurities, and that variation effects chemicals of all grades.  Other factors, are the size of "teaspoons" used in the mixes and the volume of water used in the mix.  Do you use calibrated scientific equipment?  Do you keep your chemicals stored at 0% humidity?  I don't.

Unless you aren't springing for laboratory analyses then the inaccuracy from purity of low  grade reagents may be smaller than the problems with the analyses.  In my experience even laboratory analyses are not usually more accurate than 2-5%.  The accuracy of even high-end test kits is worse than the impurity in the reagents.  "Low-grade" chemicals may be 90% the product that you pay for, but that is only a 10% error.  Can your test kits tell the difference between 0.9 ppm PO4 and 1 ppm PO4?; how about the difference between 9 ppm NO3 and 10 ppm NO3?  Between 18 ppm K and 20 ppm K?

The bigger factor is that we don't really know -- and realistically shouldn't really care -- exactly what the dose is.  Why worry about +/- 5 or 10% when the target level can be +100% or -50% without causing your plants or fish to flinch?

That said, I still prefer to avoid using agricultural grade chemicals.  I don't like the solids they usually contain.  There are lots of "technical grade" and UPS grade reagents out there that are cleaner than agricultural chemicals.  In at least some cases you can get an MSDS from the manufacturer that will tell you what the purity is and exactly what the impurities are.  If you're worried, then do the research.  Knowledge is a good thing.

Roger Miller

Technique, technique, technique -- Isabella Guerin, 2001

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