"Akvaristen" wrote in message et...
Three days after, the mixing tank with 32 gl tap water and peat moss has
pH=6.4 and KH=6 or 71 mg/l of CO2 according to Chuck's table
(http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm). The water is quite
dark.
How big/small a water change should I attempt next weekend without stressing
the inhabitants of my tank - I wonder? Or should I forget about it and go
buy a CO2 system?

Peter.

What's your goal? Plants? Or fish? Or a little of both?
The plants by themselves take good care of the fish, the lowered pH
from using the CO2 will perhaps help some. Not much IME.
Your CO2 levels are not 71ppm. The humic acids are keeping the pH
depressed and you are adding something _other_ than CO2 to lower your
pH. Then the KH/pH/CO2 table does not work well.

If you want to find the real CO2 content of this water let it sit out
for 12-24 hrs and measure the pH/KH.
Get some tap water and do the same thing.

Subtracted the peat water from the tap water.
Both waters will have exactly the SAME CO2 at equibrium. Equilibrium
= two glasses of water sitting out for 24 hrs.

Hard and soft water have the same CO2 levels at ambient room temps
equilibrium. So if you add/treat the water, you should be able to see
the difference from the tap.

The result from the subtraction is the effect of the humic acids on pH
and also gives you the error of your CO2 reading when using something
other than KH(HCO3) and CO2.

Sneaky ain't it?

In this manner you can use peat etc and still estimate your CO2
levels.

Regards,
Tom Barr