dwhatley;153028 said:
[base rock] will eventually become LR over time (much longer than a few weeks - Good LR has been in the ocean at least two years).
Biological filtration is all about providing a large surface area for aerobic and anaerobic bacteria to live on, and this is accomplished in many different ways in aquariums: porous ceramic, sponges, sand, gravel, sintered glass, bio-balls, cloth, etc. For every one of those methods, the bacteria colony grows from nothing to sufficient in a few weeks (assuming a food supply and water flow) and populates the surface area provided by the media. Why wouldn't that be true for the surface area provided by porous but "dead" live rock?
Yes, cultured lr is left in the ocean for years before it is sold, but is that so that it will have a sufficient bacteria population to provide filtration, or so that it will grow a lot of cool looking, and slow growing, animals and plants? People strongly prefer the look of rock with a lot of "stuff" on it to barren looking rock, and so will pay a lot more for it, but does it house more bacteria?
dwhatley;153028 said:
The PURPOSE of live rock is to start a biological cycle in your tank. If the rock is dead, it will not provide a cycle. Using dead rock in combination with LR will allow the dead rock to grow bacteria over time but it won't provide the initial bacteria to cycle your tank.
I don't think that is true. The primary purpose of live rock is to provide a place (large surface area) for bacteria to live on long term, but the cycle will start from the few bacteria in the air if food (ammonia) is present in the tank. The bacteria needed for filtration in our tanks are ubiquitous and do not need to be imported or seeded from an outside source, it just takes a few weeks longer for the colony to grow, but it will grow.
dwhatley;153028 said:
If you want me to give you a yes or no answer, my answer would be no, base rock is not an acceptable rock for cycling a tank.
I'm not an expert, but I'm skeptical about this claim. Sure, if the bacteria colony is transported intact from the ocean to your tank, in the expensive live rock, then it need only recover from the impact of travel, which would be faster than regrowing from nothing, but the slow way still only takes a few weeks (8 to 15?) as demonstrated in all other bio filtration methods, which all start with "dead" bio-balls, sand, ceramic rings, etc.
dwhatley;153028 said:
Foundation/base rock is not well defined and I would ask for a clear definition from the supplier before purchasing. Usually it will be dead rock (as in returned rock/dead rock that has been allowed to dry) and may or may not have been cleaned.
I agree, but my worry about base rock isn't that it is "dead", it is that it may not be as porous as live rock, and so may not provide living space for as many bacteria. Live rock doesn't weigh as much as other "rock" because it is so porous. Ask the supplier if an equal sized piece of the stuff they are selling as base rock, weighs the same as the more expensive live rock. If it is heavier (less porous) then it won't work as well for filtration, but it it is just as light, then it will (after a few week longer) (make sure that both are wet and water-logged when weighed, or the weights won't be comparable.)
I live in San Diego, and I could collect rocks from the ocean that have been there for centuries, and have lots of cool things growing on them, but they would provide almost no filtration in my aquarium because they are dense, non-porous, rocks, that can't house many bacteria.
My advice is that if you have more money than time, then buy the expensive live rock, because it looks better, become it will be useful sooner, and because there may be something I'm missing about the value of 2+ year old live rock.
On the other hand, if one has more time than money (an extra 8 weeks or so?) AND if the base rock is just as light (porous) as the expensive live rock, then go with the base rock, and maybe a couple pounds of live rock rubble to seed the tank with (not required, but an easy and cheap way to save a couple weeks)