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Re: Aquatic Plants Digest V3 #57

On Fri, 30 Jan 1998, Steve Pushak wrote:

> Date: Fri, 30 Jan 1998 01:42:48 -0800
> From: Stephen Pushak <teban at powersonic_bc.ca>
> Subject: boron concentration
> I'm working on a nutrient dosing formula which does not contain iron to
> be used with peat+soil substrates so we won't be adding the traditional
> trace nutrient mixes. The element I'm worried about is boron. The
> concentration in our Vancouver water is not detectable which means its
> less than 0.04 mg/L What are typical values for boron concentration in
> places which don't have tap water almost like rain water?

Average for lakes and streams tends to be around 0.10 mg/l.  Most water
supplies will be from lakes or streams.  Ground water can be higher.  My
local supply (ground water) is about 0.30 mg/l.

> I've been searching through the archives looking for information on
> boron which can be gotten from boric acid (H3BO3) or borax
> (Na2B4O7-10H2O). I also was curious about borosilicate which might be
> less soluble and suitable as a substrate additive. My dictionary says it
> occurs naturally. What's the solubility of borosilicate?

Boron occurs naturally mostly in sodium and calcium borates.  I don't know
of any natural borosilicate; I've only heard the word "borosilicate" used
in reference to a type of glass.


> What is the range of concentrations that would be acceptable for boron
> in aquarium water? What are the consequences of boron toxicity in plants
> and fish? I read in the APD that some vermiculites might contain
> excessive amounts of boron or fluorine; comments? Is the same true for
> kitty litter? Since kitty litter is not designed as a growing medium, it
> could be made from layer clays not suitable for agricultural use. I'm
> not saying it is but I'm sure there's a pretty wide range of substances
> that could be used to make KL.

According to EPA, aquatic animals appear to be fairly insensitive to boron
- e.g. 24-hour lethal dosages for minnows are greater than 18,000 mg/l.
While boron is essential for plants, you have to be careful with it
because boron in sufficient concentrations is also toxic to some plants.
EPA suggests that boron in irrigation water should be less than 0.75 mg/l.
I imagine that aquarium levels should be down there, too.

The EPA document I'm working from contains some very serious typos in
this section, so if someone has other information, they may want to chime

> Which would be better to use in the aquarium if it were being added on a
> dosage basis with water changes, a solution of boric acid or borax? Will
> borax or boric acid react with a solution of magnesium sulphate,
> potassium sulphate and potassium nitrate? I think I read that boric acid
> reacts with carbonates.

Many acids will react with carbonates.  You should be thinking of adding
boric acid only at very low concentrations, so it's acid reactions with
other chemicals will be very minor.

> I suppose I should use a ratio of boron to
> potassium as found in plant tissue to determine the appropriate dosage
> in water. My target is 10 ppm of K in the exchanged water. Am I correct
> in thinking that the boron is going to stay in solution and not
> precipitate?

I can't say for sure, but from checking solubilities in the CRC Handbook
I'll guess that combining boric acid with a calcium salt might produce a
precipitate; combining boric acid with a sodium or potassium would be
less likely to create a precipitate.

> Using a couple of references in the archive I deduced that
> the ratio of K to B in plant tissue is about 1000:1. With this ratio, I
> could target as low as 0.01 mg/L boron.

Keep it low to keep it safe.

Roger Miller