How big does LR have to be for dentrification?

[pomme]

How big does LR have to be for dentrification?

I am just wondering how big the live rock has to be for dentrification to occur, becuase of the oxygen gradient in the live rock small pieces will only do aerobic reactions, somaking Nitrate ( ), but then large pieces because there is no oxygern (anaerobic/anoxic) can dentrify the nitrate into nitrogen, so good for our tanks.

But as i think small pieces oflive rock, eg 3cm across, look alot nicer and are alot easier to fit together to form a reef (just my oppinion).

I was wondering if i am right in my thinking?
And if anyone has done a test or knows of a test on live rock to see what size it should be?

Thanx for you help
andrew

 

[steve-s]

I'm not sure I have ever seen anything documentation wise on it but I would suggest larger pieces. I use primarily LR for my filtration. Only a 1-1½" sandbed and no sump with a good protein skimmer.

Most of the rock I have is quite large but the size of the rock should be relative to the tank volume. Each piece in my tank is a good 10 lbs or larger in wieght but I also try to get ones that are less dense. Where the rock comes from can be equally important. Fiji rock tends to be quite dense and not the greatest for this task. Certain regions will have rock that is quite porous which will allow for some oxygen flow to create anoxic regions within the rock. Total anaerobic states within rock will not of any great benefit as the convertions of nitrate to nitrogen or CO2 will be quite slow.

Cheers
Steve

 

[pomme]

cool thanx steve, so what do you reckon i should keep it above 4"?

 

[steve-s]

I always find it hard to see these things in actually measurements so if you'll permit, basically take your clenched fists side by side and I would stick with pieces that size or larger. If the rock is porous it will greatly increase the denitrification ablility of the rock. It also doesn't hurt to have a few area's with rubble piles for better pod polulations.

Cheers
Steve

 

[pomme]

cool thanx for the help steve

 

[cmor1701d]

Certain regions will have rock that is quite porous which will allow for some oxygen flow to create anoxic regions within the rock. Total anaerobic states within rock will not of any great benefit as the convertions of nitrate to nitrogen or CO2 will be quite slow.

Steve,

How can the presence of oxygen create anoxic ("Absence of oxygen") regions?

So how do you keep nitrates at zero without anaerobic bacteria?

Is the protein skimmer alone enough?
Are you doing constant water changes?

 

[SquishyFish]

There are a couple of things to consider here...depth of the bacteria and the surface area of the rock. Which has more surface area? 5lbs of small rock or one 5lbs rock. The smaller rock will everytime. For filtration, smaller rock is better.

As far as aerobic and anaerobic, that depends on the amount of oxygen present. I have a great article on my site about how a DSB functions if your interested. It explains this very concept in detail.

Squishy

 

[steve-s]

How can the presence of oxygen create anoxic ("Absence of oxygen") regions?

Anoxic does not mean "absence of oxygen", it means reduced. It is an area that gets very little O2 and the bacteria that live within these areas are not strict anaerobes nor strict aerobes. Facultative bacteria that live in anoxic zones will convert nitrates albeit a little slower but do not render their foods in the same manner as strictly anaerobic bacteria. The end result in anoxic area's being primarily nitrogen and CO2.

So how do you keep nitrates at zero without anaerobic bacteria?

It's really no different than any other set up with anaerobic areas. Keeping the bio load acceptable and responsible feedings will greatly limit the production of NH3 and NO2 which are the sources of NO3 in the first place. My nitrates may not be zero but they never get above 5 ppm and quite honestly IME the ever sought after zero nitrates are not necessary.

Is the protein skimmer alone enough?
Are you doing constant water changes?

I do employ aggressive protein skimming in all my tanks but admittedly I rarely do water changes. I might need to do something every few months that may require a 5% change in the water but that will have no impact on the nitrate levels in the tank.

I also employ a great number of natural cleaners that help in keeping detritus and uneaten foods at a minimum. Sea cukes, stars and various snail species. Not to mention the many copepods, amphipods and mysid shrimp.

Cheers
Steve

 

[cmor1701d]

Thanks Steve,

I could only find one on-line dictionary that defines 'anoxia' as "greatly deficient in oxygen"

Every other dictionary I've consulted defines it at as at total absence of oxygen. A medical dictionary defines it as "a total lack of oxygen; often used interchangeably with hypoxia to mean a reduced supply of oxygen to the tissues."
which would in keeping with your definition.

Thanks for the clarification. I always enjoy your informative posts.