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Changing KH with KOH or Ca(OH)2

Eric wrote:

> OK. My Lamotte CO2 and KH test kits finally showed up yesterday, so I
> went a-testing. CO2 is at 55 ppm, KH is at 10 ppm, which gives pH of
> about 5.4 (not completely inconsistent with my measurements).
> So I figure the KH needs to go up and the CO2 should probably come
> down. And I think it's likely that Ca levels are low if KH is that
> low, right?

Nope, you've got GH and KH mixed.  GH reflects Ca and Mg in the water 
column.  KH reflects Alkalinity.

When I do a water change I adjust GH with CaCO3 (my tap water has 3.0dGH 
but the plants remove minerals, so I have to raise GH, then KH if necessary 
with bacarb.  Thi has the added side effect of raising pH.  Lastly, CO2 
injection produces carbonic acid which lowers pH.  It's all a balancing 
michael rubin
michael at rubinworld_com