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Re: Cation Ratio's - How Important is It?

"James Purchase" <jpurch at interlog_com> wrote:
> Re-reading Dupla's "Optimum Aquarium", I noticed once again the differences
> in ionic species ratios between what Horst and Kipper measured in their
> "mains water" and water from a stream in South Thailand (Cryptocoryne area).
>                 Mains           Cryptocoryne
>                 Water           Area
> Cations:
> Ca/Mg           83%             27%
> Na              14%             56%
> K               3%              17%
> Anions:
> HCO3            50%             41%
> SO4             30%             8%
> Cl              20%             51%
> Given the differences in local water supplies, I'm sure that people living
> in different areas would have "Mains Water" which might deviate from that
> which Horst and Kipper measured and the ratios might be different. But how
> important is it that the relative ratios as measured in Nature be duplicated
> in an aquarium?

In this case, I doubt that the ratios of Na and Cl are very important.
The higher proportion of K might be significant since K can run short
without frequent water changes or supplementation. You might also check
out Hoagland's Solution, a formula used for culturing plants which has
about the right proportions of macro nutrients. You can find it in the
back issues of TAG along with Paul K's formula for extracting nutrients
from kitchen compost.

> For example, I use R/O water in my tanks (TFC membrane), so I'm pretty sure
> that my source water is very low in TDS. To reconstitute the water and make
> it suitable for use in my aquariums, I add Kent R/O Right and Sodium
> Bicarbonate (for Alkalinity). As Kent does not give any information as to
> the ratios of the various elements in their products and test kits for Na
> and K are not readily available, does anyone have any idea of the "type" of
> water (i.e. the species ratio) that results from the use of R/O Right (or
> any other commercially available reconstitution mixture) with R/O water?

My tap water here in Vancouver is not unlike your RO water; deficient in
minerals. I reconstitute it with K2SO4, MgSO4, KNO3 and CaCO3 per the
formula on my web page. My tanks get most of their trace minerals from
the soil/clay/peat substrate and from fish food, a pinch of Boric acid
added to my concentrated mineral solution (the first three ingredients)
and once in a while, a ml of Flourish (~3 months per addition?)

Since the chemicals I use are sulphates for the most part, I end up with
relatively high sulphate levels in the water. I don't know what effect
that has however the plants do use sulpher as a nutrient.

> Or does it really not matter if the ratio of the cations in our tanks and in
> a tropical stream is different, given sufficient Ca, Mg and K for plant
> growth?

Sulpher is also important as well as nitrogen and phosphorus but we tend
not to supplement those (intentionally). I don't know what effect higher
or lower levels of S, Na and Cl might have. Cl is now considered to be a
trace nutrient but it is only required in tiny amounts and is so
ubiquitous that it would be difficult to ever have a shortage.

I suspect that Na and Cl do not have much effect on plant metabolism one
way or the other at low concentrations. OTOH, few plants can grow in sea

Steve Pushak                              Vancouver, BC, CANADA 

Visit "Steve's Aquatic Page"      http://home.infinet.net/teban/
 for LOTS of pics, tips and links for aquatic gardening!!!