I've seen references to porous rock having lots of holes, nooks, crannies. However, upon close inspection of some Florida rock, it appears quite dense even though there are bigger (pencil-size diamater) holes. There aren't tons of micro-holes (pinprick size) that I would expect from true? porous rock. My question then is, when people talk about "porous" rock being good for biological filtration, what are they meaning by "porous"?

Thanks.

–adjective 1. full of pores.
2. permeable by water, air, etc.


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Origin:
1350–1400; ME, var. of porose < ML porōsus. See pore 2 , -ous

Related forms:

po⋅rous⋅ly, adverb
po⋅rous⋅ness, noun


Synonyms:
2. penetrable, pervious, sievelike, riddled.

O.o

Porous refers to the many holes and crannies that give it surface area for the beneficial aerobic and anaerobic bacteria to live on. That's why judging rock based solely on weight isn't such a good idea. A more porous rock will likely weigh less and be more beneficial from a biological filtration standpoint.

Now I'm being dense. (Ha!)

Holes and crannies--good. But when you say holes, what size are you meaning? Riddled with pinprick-size holes (like window screens) or larger holes like a big cheese grater?

spaceship

Here is an example... Wood is porous, yet the pours are microscopic...

Same goes for good porous live/base rock...

It is light weight and you can see big pores, little pours, but you cannot see the microscopic pores...

Good porous rock will feel light for its size compared to non porous rock. Its like a sponge with lots of interior voids that will soak up water and house bacteria. Given two similar rocks the same size, usually the lighter one will be the better choice as it will support more fauna and flora.

Low density (weight per volume instead of weight alone) is a more specific term. Usually, Florida rock has been described as more dense than some indo-pacific rock. The least dense (most porous) rocks, IMO, are those made of branching sps skeletons, like Totoka rock from Fiji.

I just got done breaking down my 20H tank, and I took some of the rock outside and carefully busted it apart with a hammer. I had both Caribbean rock and regular Fiji; I could quickly see the differences in porosity between the two, both macro and micro in scope.

And the amount of varmints inside the Fiji - DEEP inside - was just amazing! There were many peanut worms, of different colors, bivalves ranging in size from pencil eraser to large almond, other worms that I wouldn't even touch, all kinds of stuff - very cool. I put much of it into my new tank.

There were none of those critters in the more dense Caribbean rock.