View Full Version : Live rock and the nitrogen cycle?

02/28/2006, 09:50 AM
I heard once upon a time that there is an ionic charge between the ammonia and something in the rock, thus the live rock works better at filtering from ammonia rather than nitrates. Doesnt sound right to me but what is it then?

Live rock doesnt seem to work very well at removing Nitrates once they are created, why is it using rock from the get go works so much better?

What makes rock work like that?

Randy Holmes-Farley
02/28/2006, 10:29 AM
why is it using rock from the get go works so much better?

So much better at what? Converting ammonia into nitrate?

Ammonia (NH3) is partly in a charged form (ammonium; NH4+) in seawater.

Calcium carbonate may have a slight negative charge to it in seawater, but whether it does or not may depend heavily on what is in that seawater.

That said, the conversion of ammonia to nitrite to nitrate is carried out by bacteria attached to the rock and other surfaces, and the nature of the charge on the rock, and any theoretical attraction of the ammonia to the rock, will have no bearing on that process. It works just as well on uncharged plastic surfaces.

One advantage is that live rock comes with bacteria on it that bioballs do not have.

it also permits some denitrification (conversion of nitrate into N2 inside of low oxygen regions in pores.

02/28/2006, 11:31 AM
OK, I guess I dont have my terms right,,, the denitrification (anerobic) is what Im most interested in.

But the real question is, why does rock work better (nitrification and denitrification) without something like bioballs making a ton of nitrates.

If you have a bunch of bioballs (and rock), you will have more nitrates than with rock alone, thats my mystery.

Randy Holmes-Farley
02/28/2006, 03:18 PM
Live rock works better for the conversion of nitrate to N2 gas because that requires a low oxygen region that can develop in the pore spaces of live rock and sand. There is no such space in a solid plastic bioball. :)

If you have a bunch of bioballs (and rock), you will have more nitrates than with rock alone, thats my mystery.

In addition to just collecting detritus on bioballs (that breaks down releasing nitrate) I detail a chemical explanation in this article:

Nitrate in the Reef Aquarium

from it on ways to reduce nitrate:

"5. Remove existing filters designed to facilitate the nitrogen cycle. Such filters do a fine job of processing ammonia to nitrite to nitrate, but do nothing with the nitrate. It is often non-intuitive to many aquarists, but removing such a filter altogether may actually help reduce nitrate. So slowly removing them and allowing more of the nitrogen processing to take place on and in the live rock and sand can be beneficial.

It is not that any less nitrate is produced when such a filter is removed, it is a question of what happens to the nitrate after it is produced.

When it is produced on the surface of media such as bioballs, it mixes into the entire water column, and then has to find its way, by diffusion, to the places where it may be reduced (inside of live rock and sand, for instance).

If it is produced on the surface of live rock or sand, then the local concentration of nitrate is higher there than in the first case above, and it is more likely to diffuse into the rock and sand to be reduced to N2."