I believe the rule of thumb is 1ml per 100 gallons.

I'll pose a corollary question then, why do other long running systems, when even feeding "lightly" and lightly stocked, always show trace amount of nitrates (namely my tanks ... or in some cases, show ridiculous amounts of nitrates)?

I'll say one thing about carbon dosing though, 3 weeks of "Polyp Laps Reef-resh" has done what a year of running sulfur could not, and for the first time in well over a year I have sub-10 nitrate readings in my ritteri tank. Wish I knew what the difference was with this tank and its resistance/resilience to denitrification... it's really weird.

Well LR must do something as I'm BB and test usually 0.0 or 0.2 NO3 (or got a bum Salifert testkit).

Tony, does your theory about different rock perhaps come into play here? Maybe your rock is not porous enough?

And I believe this is typical of many (most?) tanks. Isn't it?

I beleive it is fairly typical... except for perhaps in more heavily fed tanks at least...

Yeah, I'm wondering about porosity. It's funny that you started this thread because I was basically wondering the same things and the thought had occured to me just today about the rock density.

Well, I've gone through bouts where I've fed really heavy, no change in NO3. Maybe I'm just lucky?

I guess I bring this up now after that comment I saw, and the fact I need to buy new rock in th enext few weeks.

Nitrate is removed with water changes but more importantly organics are removed before they break down into nitrates with a good skimmer. Also a refugium can work fairly well at removing nitrates. I really doubt your rock is doing very much, maybe some but very little.

If you're looking for some good information on the subject try researching waste water treatment, denitrification is a necessary part of this. There's not a whole lot out there for info regarding this in the aquarium.

ok, but after 2 months of no water changes, no refugium and a reasonably decent skimmer, still no detectable NO3.
Does anyone have a comparable FO tank where this happens? I gotta believe the rock is doing more than you think, granted perhaps less than I think. Tony has lots of rocks and a self proclaimed NO3 problem, so whati s different? He skims, changes water, etc, probably more than I do.

Let's keep the opinions coming.....