Carbonate Hardness levels (KH)
> From: Calvin Chin <cfc at pacific_net.sg>
> Date: Sat, 19 Oct 1996 00:06:29 +0800 (SGT)
> Dupla recommends a KH level of 3.5 at least, to prevent PH fulctuations they
I might be wrong, but I think they recommend 3.5 dKH so that their
Continuous Test reads somewhat correctly. In general, I've had
strange results with that little piece of equipment. A real CO2 test
might serve you better.
> Since I am using a Dupla continuous PH control unit tied in with my C02, I
> was wondering if a KH level of 2 will be sufficient. With a KH of 2, I do
> not encounter wide PH fluctuations at all and C02 level is just sufficient
> (Dupla C02 monitor gauge reads green - sufficient C02).
You might approach this from a different direction.
1. Dissolved CO2 levels should be 15-20 ppm for optimum plant growth
and minimal distress to the fish (IMHO, of course).
2. Pick your desired pH.
3. Consult a pH/KH/CO2 table to see how much KH gives you the
4. Let your controller work on that.
For example, with 15 ppm of CO2:
pH 6.6 requires 2.0 dKH
6.7 2.5 dKH
6.8 3.1 dKH
6.9 4.0 dKH
7.0 5.0 dKH