Re: Aquatic Plants Digest V2 #128

> >4) Do I have to raise the GH also? Or does it increase with the KH? If not,
> >   what level is appropriate? My fish are mostly red and diamond neon tetras
> >   (and some algae eaters like SAEs and ancistrus + corys), plants are anubia,
> >   cryptocoryne, hygrophilia, limnophilia, vallesneria, rotala.
> GH and KH are technically independent variables. 

> Testing for KH is very specific in that it measures Carbonates. 

Alas, all "KH" test kits on the market are total alkalinity tests, and will
register any number of buffer substances.  True, the dominant buffers in
natural freshwaters are bicarbonate and carbonate.  There are also a 
number of buffers on the aquarium market which are organic buffers 
(mainly Goods' buffers, a class of organic compounds synthesized 
initially to aid biochemical research and subverted for a wide number of 
ends.)  Phosphate in abundance will also register on "KH" test kits.

> GH is a non-specific test for a value that has been evolved in tradition. 

Actually, the origins of GH testing have a lot more to do with the ways 
of soap than aquaria.

> It is a gross indicator of
> "everything except water" in the sample. 

Not true.  Many things that are not water will also not register in a GH 

Examples include, but are not limited to:
buffers (bicarbonate, carbonate, organic)
ammonia and ammoniun ions

> (Same for conductivity). 

Conductivity is actually closer to "everything except water" in that it 
measures the conductivyt in water caused by ions.  So it is sort measures 
"everything ionic in water."  Too bad some ions are substantially more 
mobile in water than others.

> For
> example, a high GH could be caused by either calcium, iron, magnesium
> etcetra, or any combination. 

It is almost certainly caused by either calcium or magnesium.  The iron 
concentrations in planted tanks will not register on any but The Most 
Sensitive GH tests.  

If you want to know if the GH is from calcium or magnesium, you could 
always do the same tests that the reef people perform.  Hach has a total 
+ calcium hardness test kit that does very well at discriminating between 
Ca++ and Mg++.  Oh, for those interested, the iron would probably not 
register in the Ca++ portion of the test, because it should be ppt as an 
insoluble iron hydroxide.  It would be "falsely" counted as Mg++ in the 
Hach speciation scheme. Again, there isn't enough Fe++/+ in the tank to 
worry about confounding a GH test kit.