Hi all,
Even though sechem has endorsed the research the science behind BET absorbtion theory is sound.
I'm a bit of a sceptic about all this. I don't think BET is very relevant to biological filtration.
All the companies that try to sell you their "special" media will use some scientific justification, but they all unravel pretty quickly once you start looking at them more closely. If you want to polish drinking water in a <"
slow sand filter bed">, pumice might be quite a good media, and this might also be why Seachem decided to mention BET in their promotional literature.
The only real thing in common with all these "wonder" media is that they take a cheap base material, and then sell it for a large mark-up. There is more in this thread
<"http://www.ukaps.org/forum/threads/biological-media-please-help.28346/">.
Why pore space is irrelevant
From my point of view, I think that the concept of having both aerobic and anaerobic filtration occurring simultaneously in the filter media is a flawed concept. This is especially true of canister filters. The problem is that to achieve aerobic and anaerobic filtration in the filter, you are dependent upon the balance between flow through the filter and how often you clean the filter media.
The idea with a very micro-porous media is that the inner pores are anaerobic and within these de-nitrification of NO3 to N2 gas occurs, in the larger macro-pores aerobic bacteria convert NH3 - NO2 - NO3 (which is an oxygen intensive process) But, how are you meant to get the flow at a level where you get the mix of aerobic/anaerobic?
If all your filter material becomes anaerobic, you lose all your biological filtration and toxic ammonia levels build up. You also have the problem that you don't have any rapid response to increased NH3 load. If a fish dies, or you inadvertently add chloramine treated water during a water change, you are into a positive feedback loop where the tank water becomes increasingly de-oxygenated, leading to further fish death, more ammonia, greater de-oxygenation, further fish death etc.
Why oxygen (O16) is the magic number
In a planted system all you need to do is ensure that, in the filter, the oxygen supply always exceeds the oxygen demand. That way any NH3/NH4+ and NO2- are converted to NO3-, and the plants mop this up. It really is that simple.
When you export the plants, you export the nitrogen. De-nitrification may still occur in the substrate, and I like a substrate partially for this reason.
If you take de-nitrification out of the equation, the requirements for the filter media become much simpler, you just need a media that doesn't impede flow too greatly and become de-oxygenated. If you keep away from floss and fine sponge, you are pretty safe.
I like Eheim Substrat Pro ("coco-pops"), but I wouldn't buy them specially. If I had to buy filter media, I'd buy generic K1 type biocell floating media or "alfagrog".
cheers Darrel