Re: Potassium supplimentation

["James Purchase" <jppurchase at rogers_com>]

Eric Wahlig asks which source of Potassium he should use in his tanks - KCl
or K2SO4.

Both Cl- and (SO4)2- are naturally present in most water supplies. You don't
say where you are from, so I can't offer any information about what levels
you are likely to have in your tapwater right now, before you start
fertilizing for aquatic plants. Maybe you should check with the municipal
water supplier to determine your "base levels" of both ions.

You said that your water is soft and devoid of minerals. Here in Canada,
much of British Columbia has water like that. I found a link on the WEB
regarding Sulphate levels there, and likely effects on aquatic organisms.

[http://wlapwww.gov.bc.ca/wat/wq/BCguidelines/sulphate.html]

They quote a German study which found that the aquatic moss Fontinalis
antipyretica was affected by Sulphate levels of 100 mg/L (SO4)2-. Four other
studied mosses suffered toxicity at various levels, from 100 mg/L - 250
mg/L. However, doubt is cast on the validity of these tests.

Regardless of the concerns over the validity of the studies, they recommend
that Sulphate levels should not exceed 100 mg/L in freshwater containing
living organisms, and that 50 mg/L be considered an "alert level" where you
should monitor health of things living in the water. Sulphates aren't
usually harmful to people at much higher levels (but we only drink the
stuff, we don't live in it) but some people (and animals) can experience a
laxative effect at 500 mg/L.

So, how MUCH extra Sulphate you can add to your water would depend upon the
amount there now and the comfort level you want to provide to your plants
and fish.

As for Chlorides, some plants have problems if the Cl- levels exceed 100
mg/L Cl-. A "salt-free" human diet provides around 100 mg/day. Chloride
apparently isn't toxic to people but a lot depends on what anion it comes
with. Sodium (NaCl) would cause more worry than Potassium (KCl).

Look at your local water report to see what is in your water now before you
decide whether to use KCl or K2SO4 as your source for Potassium.

James Purchase
Toronto