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Re: Potash

On Thu, 18 May 2000, Cindy Camp wrote:

> I've been searching for a potassium supplement to
> add to my tank and came across the following product:
> Saltwater Farms:  Seaweed Plant Food 0-0-1


If you want to supplement just potassium then you might try finding
Morton's Salt Substitute (or something very similar) at the grocery store.
It is substantially pure potassium chloride, and the weight of potassium
in milligrams per serving is labeled on the container.  That makes it real
easy to figure out how much you need to add to any amount of water to get
the potassium concentration you want.

> The guananteed analysis is 1% Soluble Potash (K20) with
> nothing else listed. This product is from a hydroponics
> store and it is my understanding that they legally have
> to list the analysis.
> This seems like a good potassium supplement, but
> I am not really sure how much to dose. If it was 100%
> K20, I think I would dose ~.08 ml/gal to get 20 ppm
> of K20 but because it is only 1% K20, does that mean
> that I should dose 99*(.08)ml/gal (~8ml/gal)? Which
> is 1.8 cups of this stuff for my 58 gallon tank!
> Yikes!  What have I done wrong?  I am good at math,
> but my chemistry is horrible.

I get about the same thing you do.  1% K20 is about 10,000 mg/l of K2O.
Let's say your tank contains 190 liters of water.  If you want to add 20
mg/l of K20 to your water you will need to add 3,800 mg of K2O (that's
190*20). To get 3,800 mg from that potassium supplement you need to add
0.38 liters of the mix (that's 3,800 mg divided by 10,000 mg/l).  0.38
liters is about 1.6 cups.

I ran across something like this when I bought a reef calcium supplement
to boost the hardness in one of my tanks.  The entire bottle (which cost
something like $8) boosted the GH in the tank by a degree.

It looks to me like the reef keepers that actually buy and use those
products are *really* getting ripped off.

Roger Miller