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I'm sure a lot of this has been covered before, but I'd like to see current opinions.

When I purchased my aquarium, it was suggested that I buy a tetra "whisper" overflow unit that was inexpensive and marketed as a complete solution. It does, however, lack specific design-work for biological filtration and flow control. Recently, I've been wondering about it's effectiveness in helping to culture aerobic bacteria--which supposedly live in the gravel. If the bacteria lives in the gravel, wouldn't it need oxygen flowing through it? I've read in numerous places that the biological filtration supported by undergravel filters can instantly cease if your powerheard/pump is shut-off or stops working. This in turn is said to cause numerous problems with the water chemistry and the tank may require cycling once more. That said, I know the oxygenation coming from an overflow filter and reaching the gravel, can't compare to that of an undergravel filter.

So, where would the bacteria be living in a 'plane jane' filter like mine? On the filter element where the water's surface breaks? On the gravel in small amounts?

If my filter is shut-off, parts are removed that assist in pumping, or the water level is below the strainer.. would that mean the lack of oxygenation would kill off bacteria living in the tank?

Seems the bio-wheel types would be free of worry when it comes to power failure since the "bio-wheel" isn't submerged.. provided the product does what it says it does.

There are numerous overflow filters with secondary biological filtration, typically in the form of a sponge.. but I somehow doubt the 'biological' effectiveness of many of these filters since the element is often completely or almost entirely immersed in water.

There's also a number of inexpensive foam filters which are re-usable and attached to a powerhead or pump for operation. I've heard a lot of good things about this style of biological filtration, but I'm sure if your main filter is adequate then it's not necessary to have all the redundancy.

Any thoughts?

Hi Seattle!

Beneficial bacteria live in the filter media - sponges, BioMax etc.

Filtration will stop when any filter does, there is no water movement to filter.

If the power goes off and you lose your bacteria put in some Cycle - this should only be necessary if they have dried out though, if they have stayed wet you are likely OK. Cycle is expensive but probably the most practical way to 're-boot' bacteria in an established tank.

It's usually lack of water (being dry) that kills the bacteria, not lack of oxygen but that could happen in clogged media I guess.

Biowheel filters are I believe the worst style by reputation, the bacteria are continually exposed to open air thus dryness and they are finicky for maintenance and will stop when the power does like most things powered. Filters such as the hang-on variety or submersible ensure the media is always wet - that's the whole idea if I have it right. It seems to me the bacteria could hardly be of any benefit if they weren't right there in the water, what good are they doing outside? Thoughts?

Foam (sponge) filters are useful really only for high-maintenance small tanks such as those with fry, they just don't do the work.

In my 10 gallon I have a hang-on Aquaclear Mini and a Fluval submersible, not sure of the model number but it's the smallest. The Aquaclear has run continuously for 18 years and it is much older than that, dig this all original parts. It is rather reliable and probably your best bet for ease of maintenance and cost, also for options when it comes to media - there are many types that can host bacteria.

Good luck !

An aquaclear mini with all original parts, eh? Out of curiosity, is it close or identical to the modern version?

My brother has one and it seems like a good all-in-one unit.

As far as the wet/dry issue of bacteria cultures, aerobic bacteria need oxygen to live but the nitrifying(aerobic bacteria needed for 'biological filtration') bacteria need the chemicals(ammonia, nitrite) in your water to consume. So a little of both is necessary, but I have to disagree, I think that oxygen is more important than water passing through in this case. Although, it is probably also equally important that the water passed through is not constantly recycled while other water in the tank remains stagnant.

[quote="eyeluvzdatrout"]Out of curiosity, is it close or identical to the modern version?

It's the same - if it ain't broke, don't fix it

IMO, I would say in general that undergravel filters are not the best filtration for long term low maintenance system. The problem with undergravel filters is that it collects to much in the gravel and under the gravel, even with good routine gravel syphoning it will not remove everything. Over time you run into problem with channeling and anerobic activity where the flow of water has stopped. If you ever have torn down a tank that has an undergravel and converted to power filters or a wet/dry filter you will see the amount of detritus and debri that collect,its a matter of time before problems start occuring.

As for bacteria, they grow on any surface that has water flow and contact, aquarium glass, tubing, rocks, wood, plastic plants, etc and of course filter media. What you want is a filter material that has alot of surface area for the bacteria to colonize, so any filter will work but its the surface area of the filter material, the flow(contact time), and oxygen rich water that makes them efficient and effective. Wet/dry and fluidize filters are probably one of the best filters because of their enormous surface area and the way water, air, and the filter media work together. For samller tanks, Personally I think the aquaclears are very good filter along with the biowheels, good surface area and flow. Exposed to air is a good thing as long as it does not dry out, ie wet/dry, so on a biowheels the maintenace is import to make sure that they are spinning. As long as you provide good circulation and air into the tank to achieve oxygen saturation in the water your bacteria will function optimally.

On my aquariums smaller than 40 gallons I usually have two aquaclears on the tank along with an air stone and one or two sponge filters. Overkill, but important to have abundance of filtration and good circulation. Reason to have air driven devices is that my air pumps are all on UPS's for emergencies.

This is just my 2 cents from a simple aquarium keeper.