Live Rock vs. Dry Rock

What is Live Rock and What is Dry rock?

Live rock does not refer to a monster made of boulders rising from the ground to smash and bash. (Galaxy Quest anyone? No?) In the context of reef keeping, live rock refers to a porous rock seeded with helpful bacteria. These nitrifying bacteria serve as the aquarium’s biological filter, converting nitrogenous waste products (ammonia and nitrite) into less dangerous nitrate, which can be removed through regular water changes.

Live rock and dry rock both refer to rock intended for structural surface area for biological filtration in a reef tank. Both will harbor beneficial, nitrifying bacteria and likely serve as the primary source for the aquarium’s biological filter. The difference lies in how they start out. Live rock will come to you fresh from the sea or another aquarium. It will come literally wet and seeded with bacteria, as well as other life, like coralline algae.

Dry rock has been dried and will require seeding, or curing, with nitrifying bacteria. These bacteria will establish themselves on the rock once it’s added to water whether you jump-start them with a commercial product or just wait. The process takes time and regular water quality testing. Coralline algae and other desirables can also be seeded to the dry rock over time using small, carefully inspected fragments of encrusted live rock.

Pros and Cons

Live (wet) Rock

Pros:

• Little to no cycling – this rock will come teeming with nitrifying bacteria. Give it a chance to adjust to the new system and test ammonia, nitrite, and nitrate before you add new animals. However, it should be more or less ready to handle some s!*$ (literally) as soon as it hits your water.
• May bring hitchhikers – coralline algae, cute, benign crabs, non-parasitic copepods, and other welcome reef community members may come as a bonus with live rock.

Cons:

• More expensive – live rock costs more per pound than dry rock.
• More expensive shipping – live rock needs to be shipped wet, which means the weight will require expedited shipping.
• May bring hitchhikers – aggressive algae, red bugs, majano anemones, and more could be lurking on a hunk of live rock. They may be nearly impossible to spot and equally impossible to remove if they make it into your tank.
• With wet shipping comes risk, including the rock “dying” in transport. When added to an aquarium, the decaying bacteria and algae on the, formerly, live rock can foul the water contributing to spikes in ammonia and nitrite.

Dry Rock

Pros:

• Cheaper – buying dry rock is just cheaper before you even factor in shipping.
• Cheaper to ship/not paying for water – shipping dry items greatly reduces the weight of the package and the need for expedited shipping.
• Avoid introduced pests – no hitchhikers means lower risks to your aquarium system.
• Easier aquascaping – dry rock can be handled and placed with relative ease in a new system.

Cons:

• Longer cycling times – dry rock will take longer to seed. We’re talking weeks, maybe months.
• Initial appearance – dry rock will be very plain initially whereas live rock may come with lovely, crimson coralline algae.

When starting a new aquarium, which should I choose?

As with many decisions about your reef tank, there are pros and cons to starting with live or dry rock. Ultimately, it’s a personal decision but the goal here is to arm you with some information to help you determine the best course for you and your aquarium.

Live, wet rock will bring hitchhikers. And, like the kind you find on the side of the highway, they could turn out to be resplendent conversationalists and lifelong friend material… buuut they could also try to harvest your organs. Coralline algae may hitch a ride and make for a lovely addition to your new tank, quickly adding a pop of color as your other frags establish themselves. But, what if a couple of pyramid snails are along for the ride and destroy your gorgeous new T. squamosa before you even know what hit you? Or what if some mysterious and flesh-hungry bacteria lurk on your new rock and within a few weeks your delicate Seriatopora lose all their tissue to an insidious case of RTN. (Not that any of this has ever happened to me…) Just like picking up a highway hitchhiker, the risk might have seemed tolerable in the 80s. However, we are deep into a new millennium and can now assess that risk with much more information and historic insight.

Dry rock, on the other hand, is a blank canvas. Yes, it will take longer to seed with helpful bacteria. They say good things are worth the wait. You’ll also obtain it for a fraction of the cost and there are so many other things to spend money on when you are setting up your new tank. Personally, it’s dry rock for me every time.

How long does dry rock take to become “live”?

The process of dry rock becoming “live” can vary quite a bit depending on the circumstances. If you add dry rock to a new system, your rock will populate with helpful, nitrifying bacteria as your tank “cycles” [link to tank cycling article?]. Adding commercially available bacteria to jump-start this process can generally shorten your cycling time but you are likely still looking at weeks, not days before your rock is alive and your tank is ready for nitrogenous waste-producing organisms. How can you tell if your tank has cycled? Routine water quality testing for ammonia, nitrites, and nitrates. Check out CoralFrags.com’s articles on this topic to learn more!

Adding dry rock to an established system, one with an already healthy and thriving biological filter teeming with those poor hungry microbes, will greatly reduce the time it takes to animate your rock. Adding a new rock, new surface area for your bacterial besties, can be a great idea if you are struggling to keep your ammonia or nitrite levels in check. Also, not a bad idea if you are planning to add more animals to your system (say some beautiful new coral frags? *wink wink*). Get ahead of the increased bioload by increasing the capacity of your biological filter.

Pests on Live Rock

There are so many things to worry about when introducing anything new to your reef tank. With wet live rock, there is very real potential for undesirable hitchhikers. Aiptasia, majano anemones, Asterina sea stars, pyramid snails, bristle worms, any number of encysting parasites, insidious algae, and predatory crabs are just a handful of the horrors hardy and stealthy enough to hitch a ride on live rock. Many of these pests prove almost impossible to remove once they enter your system. Proceed with extreme caution. If you do decide to go the live rock route, know and trust your source and thoroughly inspect and quarantine each piece before adding it to your aquarium.

Conclusion

It is definitely possible to obtain live rock from a safe and reputable source; a friend whose fastidious husbandry practices you know and trust, another tank in your own menagerie, a bio farm (a system set up just for seeding rocks or other biomedia), or an online coral frag retailer with an impeccable reputation. If you choose the live rock route, just do your due diligence. It is definitely the easiest way to jump-start your biofilter and comes with a handful of other potential benefits discussed above.

Dry rock comes with a lot less bacteria but a lot less stress and less strain on your budget. It’s the safer option for sure and the one I would recommend to avoid major problems down the road with your reef aquarium.