[APD] Re: Wet Dry Filtration in a Planted Aquarium?

[Clint Brearley <clint_brearley at telstra_com>]

Well, if the plants are growing well, the water coming into the filter will be saturated with oxygen (and the O2 *needs* to be dissolved for the bacteria to be able to utilise it). But the limiting nutrient for the bacterial population size would be ammonia anyway, not oxygen. In fact for any sort of biological filter, theoretically, oxygen and surface area for bacterial attachment only need to be in slight excess of the ammonia supply for the filter to function effectively. The extra surface area and oxygen offered by a conventional wet-dry just adds extra redundancy to the system. Of course if you continually increase your bioload (gradually), you increase ammonia supply, and eventually either oxygen or surface area will be the limiting factor and you end up with accumulation of detectable levels of ammonia and/or nitrite. However, it gets more complicated in a planted tank cause plants use up the ammonia as well.

So in a CO2-injected planted tank, a wet-dry may not offer the same benefits as in a fish only tank, the extra biological filtration capacity is probably not needed anyway. High fish loads would probably result in severe algae outbreak long before ammonia accumulation became a problem. But they do have other benefits (hiding equipment etc) which a lot of people like. As for sealing them, well I don't think lack of gas transfer with the air would be a major problem for a plant tank. At the end of the day it comes down to the opinion of the individual aquarist. CO2 gas is cheap, but having to refil regularly can be annoying so sealing the wet-dry can be an attractive option to some.

Clint Brearley
Melbourne, Australia

> I am curious ...how can Wet Dry filters be used in planted aquaria 
> w/o the
> coresponding waste of Co2?  As I understand it, by their very 
> nature W.D.
> filters  will vent Co2 gas to the atmosphere.  In order to grow 
> the massive
> bacterial colonies that make WDs more effective, there needs to be 
> mixingwith outside oxygen at the high surface area filtration 
> medium.  This is
> where Co2 loss takes place.  
> 
> Assuming you somehow encase this part of the filtration chamber 
> from the
> outside air, how do you maintain high bacteria counts to keep the WD
> effective?  In a sealed chamber, is it not logical to assume there 
> will be
> a coresponding massive drop in bacterial growth to levels more 
> akin to
> those of a canister filter since there is no longer oxygen enrichment
> taking place?  If this is the case, I don't see why castrating a 
> WD to get
> it to work w/ Co2 injection is true progress.
> 
> As I understand it, only by injecting enriched oxygen into a 
> sealed WD
> chamber can one hope to maximize WD filtration and not waste Co2.  
> Comments?


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