I have had an interesting online discussion with Craig Thompson of the NSWCS regarding the relative merits of bio balls.
Craig’s points (I hope I’ve not corrupted the concepts in my paraphrasing) were:
Some bio balls are specifically designed to maximise flow of air and water, and to avoid retention of liquid
Wet and dry filters (eg: trickle filters with bio balls) are more efficient than emersed filters
The advantage of bio balls is in their ability to not only be very effective substrates for nitrifying bacteria, but also in their unrivalled ability to oxygenate the water
I do, and I don’t agree with this. On the issue of special designs, I’ve no grounds to challenge this point, though I am uncertain exactly how much specific design and testing has gone into these products. I suspect in the case of German designed products probably quite a lot. It’s worth reminding here that there are lots of bio ball products available, and designs of many are the subject of patents, so its most likely that not all bio balls are equal in terms of their three key abilities (1. surface area, 2. no water retention, 3 ability to “channel” air and water).
Wet and dry filters certainly work, I’m not denying the obvious, and if “working” can be judged by fish health and breeding they work at least as well as all other kinds of accepted filtration. The question really then becomes;
Are they more efficient than emersed filters as the bacteria living therein have access to greater O2 from the atmosphere?
Atmospheric air contains 21% oxygen, in comparison the amount in freshwater aquarium situations is around 8 ppm (8 mg L-1) (which varies with temperature and TDS). This means that bacteria in trickle filters are in closer proximity to higher oxygen levels (as atmospheric oxygen is dissolving into the water as it flows through the trickle filter). Does this actually makes the trickle filter more efficient? I’m not sure that this has been tested rigorously. My main concern lies with the the relatively limited amount of organic nitrogen available. The bacteria in fish tank filters use organic nitrogen as an energy source so they are presumably limited by nitrogen, as well as oxygen, availability. If this nitrogen limitation does occur, it is probable that the bacteria in an aquarium are limited to a given (albeit large) population size. This might mean that a corner filter (with it’s massive surface area on the filter wool) has approximately the same numbers of nitrifying bacteria as a wet and dry filter (in which the bacteria may simply be more widely spaced). To add extra confusion to the topic, we know very little about the species of bacteria which colonise fish tank filters, this being so - it’s plausible that different communities of bacteria occur in environments of differing moisture and oxygen availability (ie: wet and dry vs emersed filters).
Trickle filters (of any kind, not just those with bio balls) provide increased oxygenation (as the water is given a larger surface area for oxygen to dissolve in). The increased surface area of well designed bio balls presumably maximises the amount of oxygen dissolving into the water. This could be of significant importance to cichlid species with high oxygen demand such as goby or rheophile cichlids. In addition, for aquarists who overfeed and have problems with “surface films”, trickle filters and bio balls therein provide a useful means of control.
On the other hand, fish grow accustomed to a certain level of oxygen, and fish keepers with trickle based, high oxygen systems are known to have greater problems in black outs with fish dying due to oxygen deprivation than those people with lower normal oxygen concentrations in their aquariums.
My main complaint with bio balls is the price. Essentially we are talking about a plastic ball - the cost of construction of such an article must be very low - and yet the final product is quite expensive. In properly maintained aquariums, for most (see discussion above of specialised fishes) ornamental tropical species bio balls are, in my opinion, unnecessary. For individual breeding tanks, sponge or corner filters work (in the sense that the fish are healthy and breeding) and cost only a few dollars. For display tanks, particular indoor display tanks, canister filters or baffle filters are considerably quieter than trickle filters and work (again, in the sense of fish health) equally well.
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