Plants also like CO2 in the water. A high pH automatically means there
is a low level of CO2 in the tank.

No, it does not. If your KH is high, you can have a high pH with a lot of CO2.

In the end only very few plants will grow well in tanks with a high pH
- Vallisneria comes to mind.

That is simply not true. Plants like hard water, and hard water often comes
with high pH.



Leigh

http://www.fortunecity.com/lavender/halloween/881/