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CO2 & hardness help (long)
Having finally decided to attempt DIY CO2 I bought a 'Hardness Test Kit' &
spent a lot of last night testing things - with inconclusive results! Maybe
someone can help me out...
Since I started doing this back in August 99 I've only ever put tap water in
my tank &, lately, Hagen Aquaplus at each water change.
Every time I ever tested my tap & tank water it has been pH=8.2.
My tap water also tests ~40ppm Nitrates so since December I do all water
changes via an inline, salt-water rechargeable, Nitrate & Phosphate filter
(available in the UK, called a 'Nitragon'). Occasionally, after a 50% water
change, I also put the Nitragon inline with my canister filter for about 2
hours to get tank Nitrates back down to 0ppm.
I also have a sachet of a Nitrate removing resin called 'Cleanwater' & 200g
of GAC in my filter which I change every few months.
The hardness test kit I bought ('Interpet') tests for 'Total' hardness (blue
solution added 1 drop at a time to 5ml of test sample - turns pink initially
then turns blue on completion. Number of drops = degrees of hardness) &
'Temporary' hardness (orange solution, turns blue initially then turns
orange/yellow on completion. Again, number of drops = degrees of hardness).
Firstly - is 'Temporary Hardness' the same thing as KH (or Alkalinity?
What's the difference?)? I've read all about this on the Krib but it still
hasn't 'clicked' for me.
My tap water tested 9 degrees 'Temporary' & 16 degrees 'Total'. However,
for the first time ever, the pH has dropped to 7.3! That would seem to
indicate a CO2 concentration between 14ppm & 17ppm (depending on which
formula you use) unless the water company is putting some other acid in the
water. Is that likely? Although I tested the pH with a tablet based test
kit I'm sure the result is correct (see later).
My tank water (with current level of DIY CO2) tested 3.5 degrees 'Temporary'
& 15 degrees 'Total'. The pH measured 7.6. So CO2 ought to be 3ppm
(probably reasonable - I don't have a very efficient CO2 reactor & my main
filter generates a lot of surface agitation & I have an airstone).
So where did the missing 5.5 degrees of 'Temporary' hardness go & why is the
'Total' hardness unchanged?
I bubbled air into the tank sample for about 15 minutes & re-tested - result
was 3.5 degrees 'Temporary' & 14 degrees 'Total'. pH was 8.2 which I
expected & which indicates CO2 around 0.6 - 0.8 which also sounds reasonable
At this point I re-tested my tap water - pH=7.3. So I guess the test kit's
OK & the tap water really is more acidic than usual.
Finally, I tried blowing into a sample of tank water (as recommended by
someone, somewhere) to raise the CO2 to 60ppm (is that correct?). The pH
dropped to 6.4 which indicates CO2 between around 42ppm & 53ppm (using
'Temporary' hardness = 3.5). So is 60ppm not correct? (I think that info.
came from the Krib).
The same experiment done with tap water gave a pH of 6.7, so CO2 is between
54ppm & 68ppm (using 'Temporary' hardness = 9).
The one thing I didn't do (but wish I had) was to aerate a sample of tap
water & then re-test the pH.
So, to summarise the questions I have:
1) Are 'Temporary' hardness', KH & alkalinity the same thing?
2) Is it reasonable to expect (in the absence of CO2 injection) that my tank
water has dropped 5.5 degrees of 'Temporary' hardness in 4 weeks? Or, has
my recent DIY CO2 injection (about 2 weeks worth) somehow affected the
3) Why didn't total hardness (which presumably is 'Temporary' hardness plus
some other hardness) also drop by 5.5?
4) Is it likely that the 'Nitragon' filter, as well as removing Nitrates &
Phosphates is also swapping Calcium for Sodium - like a regular water
softener does (which might explain question #3 above)? If so, is that good,
bad or indifferent for the plants & fish?
5) Is it likely that mains pressure tap water has between 14ppm & 17ppm of
CO2 in it? Alternatively is there any other way the pH could drop from 8.2
(where it has been since August 1999 & February 2000 when I last tested it)
6) If you inject CO2 by 'breathing' does that give a reliable reference
point (i.e. 60ppm)?
Any ideas would be appreciated.
By the way - one extra piece of probably spurious information: After I
started using the 'Nitragon' filter for water changes & Nitrate removal, my
population of regular pond snails appeared to decline & their shells seemed
more 'transparent' than they had been. My MTS population has remained