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Something is way off - PMDD

If I calculate doses based on the 500 ml recipe (Mullins, using 2
tablespoons of K2SO4) for PMDD posted at The Krib, I get a dosing regimen
for a 90 gallon of only 1.5 ml daily at 1/6 ml per ten gallons. I realize
that Sears-Conlin didn't make fixed dose volume recommendations, but the
tablespoon method by Mullins is easier to grasp, at least by me.

If I go to Chuck Gadd's dosing calculator at:


and try to get K up to the recommended weekly dose of 20 ppm, I get a dosing
regimen that is 10 times more than the recommended PMDD, on a daily basis.
Either the PMDD recommendations are way low, at least for K, or the
recommendation to dose K at 20 ppm a week is way too high.

I'm using Chuck's calculator to figure dry dosing by entering "1" as the
number of milliliters of water in the solution, it gives a good answer even
though you could never really dissolve the powders in that little water. For
example, for my 90 gallon, I'm now dosing 1/4 teaspoon a day of K2SO4, which
is 1.98 ppm per day, or about 14 ppm per week. (Once I start dosing KNO3
again, I figure the extra K in there will make up the difference.) If I
dosed based on the PMDD recipe recommendations, I'd be dosing less than 0.20
ppm per day.

It seems to me that if the PMDD dosing is that low, then K would become a
limiting factor rather than P. Also, it is nearly impossible to dissolve
very much agri grade K2SO4 in 500 ml of water, so the actual PMDD dose is
probably half of what the calculations indicate. If Chuck's calculator is
accurate (and I'm not suggesting that it isn't) then it is a powerful tool
to determine dosing - thanks again Chuck.

Tom Wood
Austin, Texas, ya'll