It was something to do with it being porous, he was saying about the cycle being amonia >> nitrite >> nitrate just like the filter does....
Totaly agree with andy here really. Yes, porosity allows for more bacteria, otherwise known as surface area for colonisation. Yes, the cycle goes something like Ammonia > Nitrite > Nitrate but to futher reduce nitrate, you need to create an anearobic zone, IE area without the presence of oxygen. Tufa rock has been known to cause nitrate, not reduce it. In marine aquaria (I know its going into FW) tufa rock isnt a recomended source of filtration. To make that form of rock work in a FW tank, youd need flow. Like the 20X turnover andy has mentioned. It might work to reduce nitrite and ammonia if you have enough flow. Give it a shot like your going to in a QT and tell us the results.
then it does another step which I can't remember and that keeps your nitrate levels down and reduces the need for water changes just like in marine tanks where you just top up instead of taking water out.
I just wanted to clarify this, marine tanks, even with the use of Live rock, a sump, or a refugium, still require water changes. It is highly recomended, and many top level aquariums and well known reefers swear by their water changes. They are essential in removing any unwanted pollutants, and adding benefcial ones which ar gradually reduced and consumed by macro algae and corals etc.
We top up water soley to keep salinity stable, and replace water from evaporation. As water evaporates, salt remains in the water body, so your tank gradually becomes more and more saline. Using freshwater top-up prevents the tank reaching dangeroulsy high salinity levels.
So basically its just like FW tank maintenance. 20% + water changes weekly or bi-weekly (fortnightly) and FW top-up daily if need arrises.
