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Re: Biowheels-CO2-plants redux

Tom, Shannon, Karen, et al, thanks for your input.

> A biowheel creates a relatively large water-air
> interface which provides the opportunity for the "excess" CO2 molecules to
> leave the water and become airborne.  So, in short, biowheels defeat CO2
> injection by providing a pathway for the injected CO2 molecules to leave the
> water quickly.

I knew I was losing some CO2 via the biowheels, but just didn't know if the
loss outweighed the overall benefits. Since I was getting acceptable CO2
readings with them on (probably since I slowed my wheels down) I didn't want
to ditch them without justification. You'll note I say "was," because I'm
currently experimenting with them off for comparison of water chemistry with
them on. So far, I have more CO2 (duh), possibly even too much; getting
around 25mg/L in the AM with a .7/sec bubble rate. Since I can't really slow
my yeast generator without risk of spraying the walls with a Zima-like
substance <g>, maybe the biowheels could serve as a regulator for the CO2

> Unless you are keeping a high fish load, or can't keep the
> plants growing, the plants are a better filter than the bacteria on the
> biowheels anyway.

Oh yeah, forgot to mention that. I have about 50 community fish (most an
inch long or so) in this 45 gal. Is this high or low?

> OTOH, bio-wheels are _strictly_ biological filtration, so they compete with
> the plants for nitrogen.  If your tank is over stocked or under planted,
> they will give you a margin of error.  If you are having trouble keeping
> the nitrate levels up in the tank anyway, biological filtration is more of
> a nuisance than a help.  (If you have to change water to keep your nitrate
> levels reasonably low, you probably benefit from the bio-wheels, if you
> have to add nitrogen, remove them)

Is the consumption of nitrate by the bacteria really significant? They seem
to have left enough for the algae. BTW, can anyone recomment a good,
sensitive, accurate nitrate test kit?

> They become more of a problem when CO2 rate drops, unless it drops to the
> point that CO2 in the tank is LOWER than at equilibrium with the
> atmosphere.  Then, again, the biowheels could help alleviate that
> situation.  But if your CO2 level is that low, you probably have other
> problems, or a _really_ slow growth tank, in which case the biowheel _and_
> the additional CO2 are probably superfluous.

Couldn't fast growth rate in a densely planted tank cause CO2 levels to
temporarily fall below equilibrium by "sucking" up all the CO2? Most of the
time my CO2 levels are above equilibrium (usually over 10), but on occasion
they will drop to below 5. (Like when the CO2 generator is about spent--less
than 1 bubble every 3 secs.) Or are you referring to other possible causes?

Dan Dixon