jfinch wrote: It could be that if nitrification is occuring in a location where it's possible for denitrification to occur then there is a greater chance for denitrification to happen.  i.e. there will be a greater "local" concentration of both nitrate and H+.  Since it's unlikely that a wet-dry filter will house many denitrifiers they lead to higher nitrates.

I disagree with Jon on this one (although Jon is much smarter then me).  I believe it is similar to the second reason he mentioned:

A wet/dry is just too efficient.  It gives plants, corals, clams, etc. no time to intake the ammonia and nitrite because it is almost immediately converted into nitrate.

Adam Blundell wrote: Jon, I do like that concept, but am not sure it works.  However, it is one of my main reasons for promoting larger sized irregular shaped substrate, and not small little round sand. Eventhough I'm not sure how much it works.

Don't listen to Adam.  He has this crazy idea about large irregular shaped substrate.  It's crazy.  Forget it.  He couldn't even get Dr. Hovanac do agree with him.

Adam Blundell wrote: The problem is that most people think of wet dry's and say "oh that doesn't work".

I've never heard anybody say that wet/drys don't work.  In fact I think wet/drys are the filter of choice for fish only tanks.  What I have heard people say is that wet/drys don't work well for reefs because they are a nitrate factory (which in fact they are, but that doesn't mean you can't use them on a reef). 

rstruhs wrote: I just received my new catalog from Drs Foster & Smith.  On page 17 they have a Nitrate Reductor for $200.00.  Does anyone have any experience with this type of filter?

These do work, and IME work better then the coil denitrators that Jon mentioned, but I would spend my money on a nice refugium, more live rock, etc.  Do you have a Nitrate problem?

I've never used or seen that unit.  I have used a coil denitrator in a freshwater system.  I had less then spectacular results with mine , but I think they can and do work for some people.  The key to these kind of units might be feeding the bacteria, but I'm not sure.  Either way, in a reef system, I'd rather spend the $200 on more live rock.

I just received my new catalog from Drs Foster & Smith.  On page 17 they have a Nitrate Reductor for $200.00.  Does anyone have any experience with this type of filter?

Here is a link to their site with the information on the Nitrate Reductor, or you can search their site for item # MA-195475

http://www.drsfostersmith.com/product/prod_Display.cfm?Catal ogCustomerNum=&catalognum=&pCatId=4567&prodId=85 81&catId=1018138&siteid=6

Jon,

I do like that concept, but am not sure it works.  However, it is one of my main reasons for promoting larger sized irregular shaped substrate, and not small little round sand.

Eventhough I'm not sure how much it works.

Adam

I love these kind of topics.

It could be that if nitrification is occuring in a location where it's possible for denitrification to occur then there is a greater chance for denitrification to happen.  i.e. there will be a greater "local" concentration of both nitrate and H+.  Since it's unlikely that a wet-dry filter will house many denitrifiers they lead to higher nitrates.

It could be that a good portion of your nitrogen export is being done by the plants (and corals) in your tank before the ammonia and nitrite are even converted to nitrate.  I think many if not most plants will preferentially uptake ammonia over nitrate.  When you use a wet-dry you speed up that last nitrification step (nitrite -> nitrate) making the plants consume a less desired form of nitrogen.  This scenario puts less importance on denitrificaiton and more on "ammonia uptake" of organisms.

It could be some other mechanism.

One topic I have been reading about (in my spare time ) is denitrification by biofilms.  These biofilms can be less then a micron thick and contain anaerobic regions under the film.  I asked Dr Tim about this and he kinda poo pooed the idea, but there are litterly 100s of references to this.  Here are a few:

http://www.wrc.org.za/publications/watersa/1999/July/jul99_p 357.pdf

http://www.postech.ac.kr/ce/great/publication/interjour/inte rjour37.pdf

http://journals.tubitak.gov.tr/engineering/issues/muh-98-22- 1/muh-22-1-6-96098.pdf

http://www.cee.vt.edu/program_areas/environmental/teach/wtpr imer/treatmen/treatmen.html

I think you're right.  The problem is that most people think of wet dry's and say "oh that doesn't work".  Bull crap.  It works wonderfully well (is that even a word).  It breaks down ammonia to nitrate like a champ. 
But what you need to know is that it doesn't do denitrification, and you still need some way to do that.  Like a deep sand bed, or water changes, or whatever.

Actually, for the most part, nitrate is viewed as the final product.  Denitrification is a wacky area that a few hobbyists (the vocal ones) like to talk about.  For most people getting nitrate is the final step.

Adam

I've been reading about nitrates and wet/dry filters and have a question or two.

The wet/dry type filter (or a mechanical filter of any kind in a high oxygen environment) does a good job of converting waste to nitrate, but the nitrate builds up because the bacteria that remove nitrate need anaerobic (or close to it) conditions.  Is that correct?

So if you have a wet/dry type filter (or a power filter with filter floss and maybe carbon in it) and you have a DSB (sufficiently fine and deep to give anaerobic conditions) and live rock, wouldn't the nitrate level eventually drop to zero (or close)?

I've read (and the people writing this admit they are oversimplifying) that the "speed or efficiency" at which the nitrate is created by a wet dry filter prevents the anaerobic bacteria from getting rid of the nitrate.  Why?

Can anyone point me to a good article about this?

Thanks!