Re: Last question before investing in the CO2 system...

[Roger Miller <rgrmill at rt66_com>]

Diane wrote:

> I've read in a couple of places that CO2 may not be required in a heavily
> stocked tank, since the fish and their waste are providing more input to
> the system;

That's a theory.  I doubt you'll find many people on this list who could 
claim long-term success from providing CO2 with high stocking levels.

> but on the other hand, most of the really spectacular
> algae-free planted tanks have relatively low fish-stocking levels, and CO2
> added.

If for no other reason, this could be because the owners of those tanks are 
concerned about the health and beauty of the tank  Overstocked tanks tend to 
be neither real pretty or very healthy. 

> To put it simply, then, is the problem that if you put in enough
> fish to generate CO2 equivalent to adding it from a tank, that you also
> inevitably put in too many other nutrients too (particularly phosphates?),
> which increase algae growth at the expense of the plants?

There's a real problem getting things to balance out.  Forget about the other 
nutrients and just try to work out the balance that you need to strike 
between CO2 and oxygen, with a big fish load, lights on and lights off. 

Get that one worked out and then you can worry about the other details.

It's a lot better for the fish and plants if you keep the fish load moderate 
to light then provide the plants with a little extra CO2 to keep them growing 
happily.   Further, if you keep the lighting at moderate levels then you have 
a lot more flexibility about how and how much CO2 you need to provide. 


Roger Miller