live rock: how porous is too porous for filtration capabilities

[mc-cro]

Everyone knows that live rock is good for natural filtration, and it is the bacteria that are down deep in the anaerobic (oxygen free) areas of the rock that do all the converting.

It is also commonly said, that more porous rock is better lb per lb for filtration capability. ( although I am not sure of the exact basis for this)

On the other end of the spectrum, many people also say that live rock rubble really does not offer that much filtration capability, because it is so small that it doesnt really contain any enaerobic areas.

So, take a very porous rock, like BRS Pukani rock, it is very light and porous, so much so that in my opinion, it is close to the same make up as live rock rubble. How good is pukani for actual filtration capabilities? I only have about 60lbs of dry pukani in my new tank, (total system of 200g), and while I sit here and wait for the tank to cycle, I am beginning to wonder how well the pukani is going do for filtration.

[RotaryGeek]

Plenty of people use that rock with excellent result. I would worry about.

[dublo8]

From my understanding it's the surface area. I'm not sure what is incorrect or correct about some of those theories or if they are theories at all. In sure there may be truth behind some of them. The bacteria populates the rock surface. If a porous rock has more usable surface area than a solid smooth rock I would assume it's better. I use the brs rock but unfortunately I haven't sat down to get a census on my bacteria population lol.

On a side note. If my statement about bacteria on the surface is true, wouldn't coraline algae covering every nook and cranny be disruptive to the population?


Sent from my who cares they all do it now.

[mc-cro]

I am pretty sure its the bacteria that is inside the rock, not on the surface of the rock. but I may be mistaken.

for instance, right now I have about 20lbs of live rock rubble in my sump on my frag tank/temporary holding system. Plus about 10-15lbs of regular live rock, and I have to keep a close eye on nitrates, even with only 3 fish. Previously I had over 150lbs of live rock, and never, ever, in 10yrs had a nitrate problem no matter how heavy I stocked, or how lazy I got about maintenance.

[NanoReefWanabe]

Originally Posted by mc-cro

I am pretty sure its the bacteria that is inside the rock, not on the surface of the rock. but I may be mistaken.

the bacteria is on the surface of the rock...every surface of the rock...the more porous the rock the more surface area it has therefore the more bacteria...

coraline coverage wont effect the growth of bacteria as there is more then one way for the bacteria to get into the rocks...

[mc-cro]

Okay, working under that assumption, then why is it said that live rock rubble does not provide the same denitrification as regular live rock. And also why does a DSB with its anearobic zone also contribute to the denitrification process?

[mc-cro]

found this in an article in ReefKepping magazine by Shimek
http://reefkeeping.com/issues/2004-0...ture/index.php

Assumption 2: The Interior Of The Rock Contains Denitrifying Bacteria

This is probably the easiest of the assumptions to validate. Most authorities (see Capone, et al., 1992) consider that such bacteria are ubiquitous. They are likely found in virtually all habitats at least in small numbers, but thrive in almost all areas where the conditions are to their liking. The inside of the live rock would be a good place for them, and it appears that they are probably there (Risk and Muller, 1983). It would seem that the assumption that live rock contains the appropriate denitrifying bacteria is therefore valid.

[Khemul]

Originally Posted by mc-cro

Okay, working under that assumption, then why is it said that live rock rubble does not provide the same denitrification as regular live rock. And also why does a DSB with its anearobic zone also contribute to the denitrification process?

Because at a certain point in the cycle the bacteria stop liking a lot of oxygen in their environment. You get that low-oxygen environment deep inside the rock or under a lot of sand.

[Frogmanx82]

I would say the rock is too porous if water flows through it easily. The low oxygen areas need low flow to develop. I suppose rubble would work in a low flow area of a tank. Lots of times though people talk of using rubble in a sump and then it would act just like bio balls, making nitrates and no conversion to nitrogen.

[dh350twin]

very interesting...tagging along for this.

[billdogg]

y'all are confusing aerobic and anaerobic bacteria. Both can help with the denitrifying process and both are present in our systems.

[mc-cro]

you are correct, but I am specifically asking about the anaerobic bacteria in very porous rock that may only have a couple inches at most of solid rock between branches.