Live Rock Theory

So my first saltwater tank finished cycling about a week ago (humble 29 gallon) and I'm hoping to get fish soon, probably two clowns to start. I've got a good bit of live rock, probably 15 lbs of live rock and 45-50 lbs of dry rock. We just finished moving into a new house this past weekend (part of the reason no fish yet, wanted to watch for any die-off) and I just found out my roommate's parents have a much bigger tank w/stand (not sure the size, they just said 'a lot bigger than that') in their attic that they said I can have/use.

That got me thinking about the theory of live rock. I think the going concensus is 1-1.5 lbs of live rock per gallon, but more is better than less and can support more fish. My question is, do any of the people more confident in the theory of live rock take into consideration the porosity of a rock when estimating it's contribution to the tank's total biological filter? For example, one of my pieces of live rock only weighs about 5 pounds, but it looks like 75 pencils rubber banded together with washers around each pencil that ensure the entire pencil is exposed to water. And it's BECAUSE the rock is so porous that it weighs so little, even though it has the surface area of about 5 bricks or so (which would weigh ~25 lbs). When I picked it out, I was hesitant because it seemed so obvious I'd want the most bacteria for my buck and wouldn't want to pick up a bohemoth that weighed 18 lbs (at $7/lb; no thanks). You better believe I picked up that sponge and let the 20 gallons of water it contained drain out before letting them stick it on the scale.

So have any reputable hobbyists taken a leap and offered up a formula that take into account these ideas? Because it seems to me to be a significant issue. If weight alone is factored, a person could take 50 pounds of relatively unporous rock and have MUCH less surface area than someone with 20 pounds of extremely porous rock. This factor would lend dramatic flexibility to someone wanting to experiment with less typical aquascapes.

 

Most online sites sell different types of rock at varying rates. The most pourous being the most expensive per pound. Local places probably get by without doing something like this due to lack of supply, lack of supply choice or simply local ignorance of the topic. Petco close to my house sells "live rock" at $8/pound and it just looks like a big rock out of a parking lot.

This is why I have become convinced that the proper way to do things is to have a small amount of live rock and fill the rest in with base from from a reputable dealer. BRS, Reef Cleaners, etc. They consistently deal with people who are looking for top dollar rock and they know precisely how to appease them. My tank came with some live rock and I ordered more from Reef Cleaners....I was very happy with my order and I did not have to specify the type of rock I was after.

 

going to hitch on here looks like an interesting discussion.

that was the route I took as well some of my biggest rocks are the lightest because of the density. I look at it that the more porous a rock is the more surface area that bacteria can get into.

Maybe 20% of my total rock base was purchased "live" the remainder was just base rock that I put in during the process. It's so much more cost effective with the same outcome.

 

To answer your question, yes porosity has been considered; and while the "pounds per gallon" rule is still being supported by some, it holds about the same weight (pardon the pun ) as inches of fish per gallon, or watts per gallon with lighting (which are still preached as gospel in certain small circles). Personally, I prefer to hand-pick my rocks at the LFS to ensure I get only the best.

 

I think we've all been there arm deep in a bin of rocks digging around for the right size, shape and density.

 

I've set up a lot of tanks with varying amounts of rock, and I think the amount needed tends to be way overestimated. You can have pretty minimal amounts of rock without issues. I have no idea about pounds per gallon or any of that nonsense. If you use reasonably porous rock and make some interesting structures (i.e. don't just stick one rock in a tank), usually it's plenty.

As for live rock vs deadrock. I also don't think it matters, I've set up tanks with all dead-rock and just a cup of sand from an established tank, and within 6 months to a year, looks the same as if I had used all live-rock. A cup of sand from an established tank, will have all the coralline algae and infauna you'll even need IMO. Also, plenty will come in on corals, as you add them. Some people think adding LR will speed this up. Maybe to some extent, especially on the bacterial side, however, less so on the coralline algae side IME. For the most part coralline can grow incredibly fast. If it's not, and you added something from an established tank, it likely means that the conditions aren't right, or the surfaces haven't been primed, by other organisms, in a way that promotes settlement of the algae.

 

The pounds per gallon of rock was invented when the only affordable rock was crap from Florida that wasn't porous at all and weighed a ton. In fact, I think a brick would be more porous than that stuff. (It was also loaded with adsorbed phosphates and nuisance algaes which some companies advertised as the "life" in their "live rock"). Since most people are determined to overstock (BY A LOT) their tanks, you really did need quite a bit of that kind of rock to support your tank (assuming you removed your bioballs from your wet/dry).

However, times change. Now, even much of the base rock from Florida is porous and you don't need as much rock as people put into their tanks. I aquascape until I like the looks of it and then I'm done. I don't have a clue how many pounds of rock are in any of my tanks.

 

+....

 

I use as little live rock as possible in my tanks sometimes only one piece. My thoery is the less live rock you introduce the less likely it is that you will be getting unwanted hitchhikers invading your tank. I agree with everything stated here about how many pounds per gallon. I think the guy selling the rocks came up with that one.;D

 

+1 to all these examples.

I believe a more accurate, albeit, still flawed method is to look in terms of volume. You want about 50% or the tanks volumme in rock/sand/bioball/this stuff

By looking at volume you correct somewhat for density. But your stocking, feeding habits, and flow all have more to do with the amount needed than the size of the aquarium.