Hi all,
Shrimp and fry are probably more sensitive to water conditions than mature fish but the sponges seem to work well as both a mechanical and bio filter.
All though the sponge is a mechanical filter it is also a very good bio filter, as long ad you have good flow through the filter you could use gravel, it doesn't matter.
Yes that is it really, sponge is a great mechanical and biological filter, I like PPI10 or PPI20 sponges, because I'm not interested in polishing my water.
Nearly any biological media will do, all I want is that it doesn't impede flow too much, if flow is impeded the water can become locally de-oxygenated.
I came to realise that even really experienced aquarists often didn't understand this fully, with potentially catastrophic results. This was why I wrote
<http://plecoplanet.com/?page_id=829>.
I want ammonia and as much dissolved oxygen as possible in the filter, I don't want anything else.
I have watched the Tyne Valley videos many times and he is very convincing.
I've seen these as well with the wick test etc., and it is very interesting and the fish look really healthy, but it isn't really relevant to us.
In an unplanted situation you are dependent upon microbial conversion of NH3 > NO2- > NO3-, you can tell this
process needs oxygen because you've gone from 3 hydrogen ions for every nitrogen, to 3 oxygen ions, and it also needs a carbon source. The only ways you can then remove the resultant NO3 is by dilution via water changes, or the anaerobic out-gassing of N2 gas. This oxygen requirement is why the measure of pollution for water and liquid effluents is its "Biochemical Oxygen Demand" (BOD).
Marine Aquarists went away from "wet & dry" trickle filters because they are "nitrate factories", but all that really means is that they are very efficient at biological filtration. They often don't have plants, and are reluctant to change large volumes of water, and because of this they developed systems like plenums and deep sand beds to allow for anaerobic de-nitrification.
Anaerobic de-nitrification will always have risks involved because if the REDOX or ORP values become too large the whole system may become anaerobic with catastrophic results. This is why trying to have both processes happening in the same filter (via filter media with very fine pores and slow water flow) is a recipe for disaster.
Wet and dry trickle filters are the "gold standard" for biological filtration, but we can do even better than this, we have plants that take up NH3, NO2- and NO3-, produce oxygen and provide lots of surfaces (particularly in the substrate), that support biological filtration.
Plant/microbe biological filtration systems, with floating or emergent plants, are about an order of magnitude more effective than microbe alone systems, and this means that we are much less dependent upon water changes (and often have to add NO3, rather than try to remove it).
Cheers Darrel
