"Skunky" wrote in message
...

Hi

I have been battling now for a few months trying to sort out my water
chemistry.

I use pure R/O DI water, remineralised with Kent R/O Right and pH
stable. My problem is I can never seem to attain a pH of 6.8-7.0 with a
KH of around 3 degrees. Everytime I reach 3 degrees, the pH ends up
close to 8.0!

Presently, I can get the water to about 7.5 with a KH of barely 1
degree. I can bring the pH down in my tanks because I use CO2. It
doesn't appear to cause the fish any problems having the new water with
a higher pH. The TDS is the same, but I would like to increase the KH
to about 3 degrees to be on the safe side to prevent any future pH
crashes. I read in a mag the other week someone having a pH of 6.5 and
a KH of 6 degrees, this just seems impossible! I am also starting to
question the accuracy of my A.P.I KH kit. My pH and TDS are done
electronically.

My tank is well planted and blows CO2, below is the water chemistry.

Those numbers look about right to me. There is a diect relationship between
KH, Ph & CO2 levels. Kh of 3 will give a PH of about 7.45 assuming normal
atmospheric levels of CO2 (3ppm). In reality with plants in the tank the CO2
level will be lower than 3ppm and so the Ph will be higher.

You therefore need to add CO2 to an appropriate level.....

At Kh 3.37 dGH (60ppm) you need the following levels of Co2 to get the
corresponding Ph

CO2 Ph
320.8
5.5

254.8
5.6

202.4
5.7

160.8
5.8

127.7
5.9

101.5
6.0

80.6
6.1

64.0
6.2

50.8
6.3

40.4
6.4

32.1
6.5

25.5
6.6

20.2
6.7

16.1
6.8

12.8
6.9

10.1
7.0

8.1
7.1

6.4
7.2

5.1
7.3

4.0
7.4

3.2
7.5

2.5
7.6

2.0
7.7

1.6
7.8

1.3
7.9

1.0
8.0

0.8
8.1

0.6
8.2

0.5
8.3

0.4
8.4

0.3
8.5

0.3
8.6

0.2
8.7

0.2
8.8

0.1
8.9

0.1
9.0



HTH

I.