I would think that
eventually, you reach a point where plants are growing so slowly that more CO2
doesn't help plant growth, any more than overdosing fertilizer in a low-light
tank does.

Leigh

Yes, you do get to that point, but still, it allows the plants to
fully utilize all the light that's there.

Think about light "limitation"
Think about CO2 limitation.
Think about Nutrient limitation.
How do you test the effects of each?

By adding _all_the_ other_ parts to slighty "excess" for the plant's
optimum needs. Then manipulate your variable, in this case light.
High CO2, high nutrients.

For nutrients: high light, high CO2.

For CO2, high light and high nutrients.

Then you know who's doing what and what effect it has.

Since algae love high light, can live on next to no nutrients(ruling
out limiting them via nutrient limitation), adding CO2 and or lowering
the light are viable options.
CO2 affects different algae differently. Mostly negative though(All
algae can use HCO3, but only a FEW PLANTS CAN).

So limiting light slows their growth down, to the point in some cases
were
you don't need to clean the glass except once every 1-6 months.

I use a shop light(2x40W) over a 55 gallon tank with a reflector.
That's about 1.67 watt/gal. This does very well.
Nutrients levels are the same for low or high light tanks, but the
dosing required is less frequent for the low light tanks(weekly works
fine in most cases)

Regards,
Tom Barr




Regards,
Tom Barr