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[APD] Re: K+ at high or low Ca values

>From: "Steve Pushak" <teban at powersonic_bc.ca>
>Could Antonio Trmas' apparent problem with Ca uptake be caused by 
>too high a level of magnesium?

>From: "Thomas Barr" <tcbiii at earthlink_net>
>Much of what I've read suggests Mg deficiency and some do not mention
>anything about Ca++ inhibition at high levels from high K+.
>Excessive calcium can inhibit Magnesium uptake.
>Magnesium, manganese, and calcium deficiencies become more pronounced with
excess K. 

OK, which is it?

I am leaning towards Steve's hypothesis, but not necessarily for hard water
aquariums. Whenever folks are adding chemicals to the water (including
epsom salts - hydrated Magnesium sulfate), there is definitely the
possibility of overdosing. Once the plant consumes the mineral, it can take
time to eliminate the effects. I believe several of us old timers
experienced problems with indescriminant dosing of epsom salts (during our
formative years) thinking that our plants need some <g>
and we inadvertently provided too much! 
On the other hand, a quick search on the internet yielded several sites
which talk about K/Mg effects: 
eg. (1)"Excess potassium can aggravate the uptake of magnesium, manganese,
zinc and iron." http://www.hydroponics.net/learn/Deficiency_by_element.asp
e.g (2)  Sulfate salts [presumably MgSO4]affect sensitive crops by limiting
the uptake of calcium and increasing the adsorption of sodium and
potassium, resulting in a disturbance in the cationic balance within the
plant. .... High concentrations of potassium may introduce a magnesium
deficiency and iron chlorosis. An imbalance of magnesium and potassium may
be toxic, but the effects of both can be reduced by high calcium levels.

It is probably hard to induce Mg toxicity in hard water.
Natural water systems provide Ca:Mg in ratios ranging from 3:1 to >10:1.
The latter are generally soft and the higher ratios in harder water. 

Some of us, like me have very soft water. I avoid problems with Mg imblance
by either providing Ca and Mg thru water changes and/or with pulverized
dolimitic lime (Ag grade, ~$2/50 lb bag). The lime provides Ca:Mg in a nice
3:1 ratio. It dissolves nicely in a few hours as long as there is CO2.

Another point: please stop GENERALIZING about "effects on plants." Plants
are not all the same. At least this thread has tried to differentiate
between soft and hard water aquariums...and talked about effects on Ammania
and a few other specific plants. This is something rare to the history of
the APD. 

Neil Frank
Although I like to think of myself as a generalist, I hate to generalize.

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