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Re: CO2 in low light tank

> Tom, didn't you point out recently that added CO2 can be good in a
> (relatively) low light tank?

Yes, Claus also said a similar thing.

> Question: if the added CO2 helps to bring
> the tank to a NO3 or PO4 limited (depleted?) state, would that be
> inviting algae or worse, the dreaded BGA?

Uptake at this irradiance is limited from the light, not nutrients. Nutrient
uptake _will increase_ but not a large degree like we might see if there was
2 x the light. You would/could likely just feed the tank well and get away
with it. I'd do water changes and add herbivores just like the higher
lighted tanks. 
Dreaded BGA? I guess some folks feel that way:) Some KNO3 typically takes
care of the limitation. Adding perhaps 1/8 teaspoon ofKNO3 would take of any
issues there. A flourite substrate could likely get you around Trace
additions at this light value.

At "some lighting value" you tip the scales and it becomes _a nutrient
remover_(Nutrients < Inputs from food) rather than having N or P build up
(Nutrients > Inputs from food). This depends on inputs(fish food, tap water,
KNO3 fert's etc) and fish load etc.
How you choose to add those is really up to you.

A discus tank that has too many fish and heavy feeding can never be outpace
by the plants at any lighting level. Water changes become the only way to
handle all the N&P.

>  I don't mean that one (CO2
> in low light) will always cause the other (algae or BGA).  I guess the
> question is should one monitor NO3 and PO4 if one adds CO2 to a low
> light tank or maintain lower levels of CO2 than in a PO4-KNO3
> fertilized tank?

Much less so. Uptake is slowed by lower lighting. Less uptake, less worry,
be happy.
Tom Barr
> Scott H.