The Redfield Ratio and You.

You know, it just occurred to me this Redfield ratio stuff is interesting but not dispositive. We're ignoring a very important element. Some things use nitrate as an energy source.

That means while bacteria use nitrate and phosphate in a well known ratio to grow, some use additional nitrate to power their processes and expel nitrogen gas. The thing about these nitrate using bacteria is they live deep in your live rock and so don't get the first dibs on the nitrate. The aerobic bacteria do.

What this means for us is that if a tank is "phosphate limited," there is a place for excess nitrate to go. It goes into rock and becomes excess nitrogen gas. If on the other hand a tank is "nitrate limited," there is no place for excess phosphate to go.

We actually observe this in our tanks. In healthy tanks, phosphate tends to be the bigger problem.

I think this means while it's possible to phosphate limit a tank, there is a buffer zone where taking out too much phosphate isn't a problem because other processes will solve the nitrate problem. There is no equivalent buffer on the other side of the equation that in aware of.

I'll say this. This just occurred to me while smoking my evening cigar. The details of the micro environment are complex and I've probably oversimplified or screwed up some part of it. The underlying point however is sound. Denitrification happens in our tanks outside the Redford ratio. That means an excess of phosphate is going to be a more prevalent problem.

I think Jon Warner has said essentially this in the EcoBak thread. At one point he makes the point your system will always have nitrate if it's needed. This is where it is. It's being metabolized. When there is enough phosphate that we need more bacteria to grow, we just leave less nitrate and the anaerobic bacteria go a bit hungrier.

 

When there is low O2. You didn't mention carbon though. Organisms use carbon for energy and even the ones that use nitrate can't do so without carbon. The redfield ratio though is just the ratio found in the tissue of one sample of phytoplankton, from one place and time.... Other organisms have different ratios too and some even may shift ratios based on the environment etc..

Also, phosphate and other metals can bind to rock, nitrate can't. So, I don't quite follow that part, but I may be misreading. Nitrate can as you said be converted to a gas and diffuse out of the system, as can carbon (which can also more or less permanently precipitate out). Phosphate isn't exported unless done so mechanically, also, due to preservatives in food for example tends to intrudeced at high levels.

 

Sorry, I made an unstated assumption. I'm talking about non-carbon limited (carbon dosed) systems.

I guess my point simply is this. In a carbon dosed system like a bio-pellet system, the most likely combination to yield stable ULNS is carbon dosing plus phosphate removal. Dosing alone may get you the result, but taking out a little too much phosphate will cause no harm. Your nitrate won't go up the second you take out one little bit of phosphate too much. You have this nice fat buffer where too much phosphate removal just means a little less outgassing of nitrogen.

If you do it the other way around however, every little bit of nitrogen you remove will drive your phosphate up. Biopellets, good skimming, and GFO is, at least in theory, the best path to stable, constantly low nutrients (even if your biopellets would do the job on their own since the little bit of GFO now means you have some wiggle room neither side rather than just on one.)

All pure theory, but there you go.