Filtration tech

Filtration tech is another huge subject. What I have here are more in the nature of some modest scattered footnotes.
 
You might begin your techno education at the Krib once again and trace out the links you'll find in the "Plumbing and Filtration" section there. In addition, Bruce Hallman contributed a FAQ on aquarium filtration in general and types of filters to The Krib. 
 
Canister filters. Canister filters offer the quietest operation and the least visual clutter inside or outside the tank. By manipulating the type of media you use, they can combine mechanical, biological and chemical filtration. You'll still need to siphon debris off the surface of the gravel regularly, and you might want more powerful water current than the canister outlet offers. The main debate is "Eheim vs. Fluval," and though it seems to be a question of design and ease of use versus economy, I'm not a qualified judge.
 
Undergravel filters. I used undergravel filtration in planted aquaria successfully for years. I've given it up in favor of simpler, more natural systems. Undergravel filtration is so unsuited to the American national psyche, that I've posted my thoughts on undergravel filters on the Mis-Tech page.
 
Hang-on-Tank (hence "H.O.T.") filters. The inexpensive outside power filter that hangs on the tank rim is flexible and handy. I have a number of old Whisper filters, but if you're buying a "H.O.T." outside power filter today, you'll want to decide whether or not it should incorporate a Bio-Wheel.
 
Bio-Wheels. A development of wet/dry filtration tech, this accordion-pleated fibrous cylinder that revolves by the weight of water like an undershot mill-wheel, offers nitrifying bacteria huge surfaces and maximal access to oxygen. The Bio-Wheel was the best tech innovation of the 1990s, in my opinion. Finally, a technology that systematically dissociated biofiltration from mechanical or chemical filtration. And the technology is quite simple, derived from advances in wastewater treatment, a field that continues to inspire aquarium management.
 
The bio-wheel essentially is a condensed trickle filter. Trickle filters surfaced in the US in two F.A.M.A. articles by George Smit in 1986. The sensation that followed was largely confined to aquarists keeping marine aquaria, especially mini-reefs. Smit and other new-wave invertebrate keepers were thinking of their set-ups as captive ecological systems. Freshwater aquarists were slow to follow; we remained fixated on the nitrifying bacteria in our undergravel filters, and the only invertebrates most of us acknowledged were live foods and snails.
 
Bio-Wheels and "loss" of CO₂. If you're managing a "plants-first" aquarium, where the fish are largely decorative suppliers of carbon dioxide and plant fertilizers, and if you are keeping an artificially high CO₂ level in order to speed plant growth, then a Bio-Wheel may be counter-productive for you; you don't want a Bio-Wheel adding all that additional water/atmosphere surface where the preciously-conserved CO₂ will diffuse into the air, and you don't want the Bio-Wheel's bacterial community competing with your plants for ammonia. For aquatic plants, it now appears, have to reconvert nitrate back into ammonia before they can metabolize it. But for many of us, and especially for keepers of unplanted Rift Lake aquaria with high pH readings, where ammonia is in its toxic form, the Bio-Wheel has become an essential fixture of our tech set-up.
 
Misunderstanding "loss" of CO₂. When carbon dioxide diffusion became popular in planted aquaria during the 1990s, a new fixation on CO₂ levels in planted aquaria drew some attention away from other plant requirements, such as the intensity of light and its spectrum. In order to maintain beneficial elevated CO₂ levels in water that was being artificially infused with CO₂, you were being advised to minimize water movement at the surface, because surface exchange was diffusing the hard-won extra carbon dioxide back into the atmosphere. That makes sense; but, as a result, fishkeepers began to feel that all surface water movement and exchange of gases between water and atmosphere was undesirable in planted aquaria, even in natural situations where no artificial CO₂ was being diffused into the water. "Any fresh air contacting the water will deplete the CO₂ dissolved in the water to very low levels," warns an otherwise-dependable net writer. So CO₂ depletion is turning into a new Urban Myth.
 
The fact remains, vigorous water movement at the surface keeps dissolved gases in balance between atmosphere and water. Gases will diffuse into depleted water from the atmosphere, or they will "outgas" from water that is supercharged with the gas. This includes dissolved nitrogen, oxygen and carbon dioxide. The only CO₂ a bio-wheel could drive off would be artificially elevated levels of CO₂ — which you might be inducing on purpose, of course, to benefit the plants. The individual saturation points for each gas depend partly on the temperature of the water, a phenomenon you already know. If you are concerned about CO₂ levels in the water, and want to increase carbon dioxide and oxygen levels, the easiest way is to turn down the heater. Cooler water contains more oxygen -- and more carbon dioxide too. The one gas does not drive out the other, by the way.
 
A note about impellors. After years of use an impellor can develop a corner nick on one of its blades, and that can result in rattle and chatter. Why didn't somebody suggest to me years ago that it's quite cheap and easy to replace the worn impellor? It never occurred to me. See why I refer you elsewhere for tech information generally?
 
Inside filters: sponge filters. Though I started fishkeeping in the 1950s with a corner filter that sat inside the tank, a type of filter that's now hopelessly clumsy and outmoded, there is still a use from time to time for a different kind of internal filter: a sponge filter running on an air pump. A sponge filter is a foam sleeve over an intake tube, powered by lift from an air pump or from a centrifugal powerhead. Any section of open-cell polyurethane foam will make an inexpensive substitute. To drill out the center or cut it so that it fits over your intake, soak the sponge and freeze it first.
 
The sponge filter never sucks up fry, and if it's been left running long enough, its exterior and interior surfaces have developed a rich biofilm. Your free-swimming fry can pick and choose at their deli and salad bar. And ammonia is constantly being processed. The sponge filter doesn't work as a chemical filter, of course. It's a modestly good mechanical filter. Particulates will collect on its surface, where Melanoides snails constantly graze. I find that with a population of snails I rarely need to squeeze out the sponge filter in siphoned-off tank water. On this heading, Harry Tolen posted at AC, 12 March 2002: "If your flow continues to decrease, it is probably because you are not abusing the sponges enough. "Rinse" is too gentle a term for what really needs to happen to them; they need to be squeezed, kneaded, rubbed, and squashed to break the detritus loose and really open them up again. "
 
I squeeze the sponges repeatedly into a bowl till the squeezings are clear. I always water houseplants with this rich dark soup: I never discard it. The sponge filter's main job is still as a biological filter, especially useful in a quarantine or hospital tank, whence you remove it, please remember, during bouts of medications. If it has been contaminated in a tank where there has been disease, leave it running by itself in a fish-free isolation tank for up to a month, if need be.
 
But don't ever clean the sponge filter, much less bleach it, boil it, nor ever let it dry out. A dry sponge filter is an item in dead storage. Store any extra sponges you have at the back of a healthy tank. When the sponge doesn't have active water flow pumping through it, facultative anaerobic de-nitrifying bacteria deep inside it will make a modest living metabolizing nitrates.
 
I keep a sponge filter constantly running in a plant nursery tank: I never know when I'm going to need a biologically mature sponge filter at short notice.