Re: Growing conditions for plants vs. algae


the tank is fairly well planted. I actually nearly ran out of space to put
the plants when I fist set it up. But since it's 2' high, not all the stem
plants have reached the surface yet. Fast growing species are Valisneria
(a whole bunch of the 'straight' ones and about 10 of the spiral ones) and
Mexican oak leaf. Limnophilia is also growing fast as well as Echinodorus
griesebachii, which is shooting runners all over the place already. Some
Ludwigia glandulosa (?) is very beautiful and growing well, just like the
Rotala rotundifolia.I also have some floating plants.  Still unidentified. 
They have nearly round leaves, about 3-5 cm in diameter and very long
roots with fine hairs. The roots are very pretty and sometimes have a
blueish shimmer to them when they break the light in a certain angle. 

CO2 and KH: I once thought that I could save CO2 by lowering KH. Maybe
some people remember the thread in sci.aquaria about adding HCl. But now
I'm not so sure anymore. It depends what you're aiming at. If you want a
certain CO2 level in the tank, say 15 mg/l, you would have to add 15 mg/l 
plus whatever is needed to get past the buffering capacity (KH). So _I 
think_ it would take more CO2 to get to a certain level of free CO2 when 
the KH is high. But my chemistry knowledge seems to have a momentary 
time-out here. Maybe it's just the same ammount of CO2 needed to reach 15 
mg/l, no matter how high the KH is. Maybe the difference would just be in 
a different resulting pH.

Of course, if you're aiming at a certain pH, say 7.0, it would take a lot 
more CO2 to establish this when the KH is higher.
The question is how much CO2 is needed to overcome the effect of KH 
difference or HCO3- concentration?