Live rock is porous rock from the ocean, commonly used as both decoration and as filtration in marine aquaria. It’s called “live” because it often carries hitchhiker organisms such as encrusting algae, sponges and worms, but perhaps most importantly, is home to the beneficial bacteria we need to properly cycle our tank. It comes in various densities and states of readiness for the home aquarium and also tends to be on the expensive side at anywhere from $4 a pound, to sometimes $7 or more. If relying on rock for filtration (and I recommend it!) you’ll want to consider acquiring approximately 1.5 pounds of live rock per gallon of aquarium water.
Cured vs Uncured
When shopping for rocks, you’ll probably see it referred to as “cured” or “pre-cured” or “uncured.” Uncured rock is rife with life which will all die off during a tank cycle. (This is good in the sense that you actually want that in order to kick things off). However, if you aren’t doing that, you’ll want to either buy cured rock or cure it yourself (preferably somewhere outside or something since it smells like low tide and you’ll be doing it for a few weeks). Cured rock doesn’t look as pretty, but is all ready to go. You can stick it right into the tank and it shouldn’t cause any issues. Also, if you’re going to cure rock and don’t mind the stench, you can cure it in your tank if you’re starting a new tank with no life in it. I’ve found the more rock you put in at once, the faster this is over with, but don’t ever do this with an established tank. You’ll cause an ammonia spike that will kill everything.
Why Live Rock?
Because it’s the most effective form of filtration anyone’s figured out. Paired with a protein skimmer, and potentially a nice deep sand bed, you can filter an entire tank with nothing else. The rock is so porous, it creates more surface area for all those nitrogen fixing bacteria to multiply in, and eat up the waste. Also, it looks really great.
Alternatives and Cost Saving Methods
The rock is, without a doubt one of the most expensive pieces of equipment you’ll have to buy when starting a SW tank. I really recommend buying as much as you can afford, but if that doesn’t work out to that 1.5 lbs/gallon I mentioned, there are some tricks you can employ:
Buy dead rock for a base. Almost any old porous rock will become “live” given enough time and seeded with some actual live rock. Be prepared to wait a lot longer than normal for this to work though. You can often get old, dead reef rock that used to be live at your local aquarium store for a fraction of what live rock costs. You’ll still need some live rock to get things seeded, but not much.
Some people oppose live rock because of ethical concerns over harvesting reef rock from the ocean. Despite laws about this being much better in recent years, and a whole industry existing now of people “farming” live rock for the trade, it’s a valid point. To that end, there are now artificially created rocks one can buy as an alternative. One brand is “Real Reef” and there may be others. I think it’s basically aragonite smushed together into rock shapes and then coated with fake coralline algae. I think it’s a great idea, however it seems to cost pretty much the same as responsibly farmed actual live rock.
Finally, while this isn’t a cost saving method, one thing I like doing with rock is building cool reef-like structures rather than just piling it up (although the tank I’m working on right now is a pile tank). You can create shapes really easily. Just get some PVC pipes, and make a structure outside the tank. (can’t seal that stuff under water very easily). Now take your rock and zip tie it to the pipes. Fairly shortly, the coraline algae will grow over it and it’ll look like a natural structure!