Re: KH Drop

[Paul Krombholz <krombhol at teclink_net>]

     * From: "Jason Rogers" <jrbruin at yahoo_com>



.......I recently changed out my old gravel and replaced it with 
profile in my 40 gal tank. The other thing I did was add a piece of 
driftwood.  Before the change in substrate my KH-PH was typically 
about pH 8.0 and KH 11 degrees (using Aquarium Pharmacuticals test 
kit).  It's been set up for 4 days now and I check the chems 
yesterday and came up with a pH of 7.2 and KH of 4.  I wouldn't even 
have checked the chems this early, but I started a DIY CO2 injection 
and wanted to see what the KH, pH, CO2 relationship looked like. 
(looks like I need a better reactor, but that's in the works) My 
question is, could it be the driftwood that is causing the KH drop? I 
soaked it for three weeks in a bucket, but didn't ever check if the 
pH of the bucket water changed.  I have read that profile raises KH 
if anything and there is really nothing else in there that could act 
as an acid buffer (no peat..).. I have read the nitrification could 
cause a KH drop, but since it is a new tank (although I kept the same 
filter media and a few rocks to help the re-cycle) this
seems unlikely to me.  Also, I only have three small fish in there 
and I never saw this KH drop before.. In fact, I've been wishing for 
more naturally softened water (I hate using chemicals for pH,KH) for 
a while, so this is kinda nice, but just a little confusing..

Thanks,
  Jason

You changed the substrate, added driftwood, and you started adding 
DIY CO2.  Of the three changes, I think the CO2 additions would have 
the greatest effect on lowering the KH.  KH is a measure of 
alkalinity, and the test is done by adding acid until the pH drops to 
around 4.2.  The test kit solution has a color indicator dye that 
changes color at around 4.2. The more acid you have to add, the 
higher the alkalinity.   By adding CO2, you add carbonic acid, a weak 
acid which lowers the pH, and, of course, also lowers the alkalinity. 
Try taking a cup or two of your tank water and let it stand for 24 
hours, which should be long enough for the excess CO2 to escape into 
the atmosphere.  Then check the pH and KH.  Both readings should be 
higher.  If they are not, then the source of the acid is either the 
Profile or the driftwood, or both.
-- 
Paul Krombholz in well-watered central Mississippi, with 
thundershowers the last four afternoons.