Understanding the function of live rock, how to ‘cycle’ your tank with it and how to setup your rock work is a fundamental component of a successful reef tank. Some hobbyists have experienced elevated phosphate levels, algae outbreaks and even coral death because of rushing past this important step in the reef systems setup. The type of live rock used in setting up your reef tank will determine the steps needed to create a balanced and stable environment for your corals and other creatures.
WHAT IS LIVE ROCK?
Live rock is the foundation of your reef system in more ways than one. First, it physically supports your corals and gives them a foundation to grow on. But it also allows the colonization of beneficial bacteria that support the complex chemical processes that take place in your tank to keep your corals alive. This bacteria is often referred to as nitrifying and/or denitrifying bacteria. These bacteria turn harmful ammonia into nitrites and then into nitrates. The nitrates are then removed via regular water changes keeping the nitrate concentrations at acceptable levels to support coral growth. The lighter and more porous the rock, the more beneficial bacteria can colonize it.
HOW DO I CYCLE MY TANK? – THE NITROGEN CYCLE.
The Nitrogen Cycle, often referred to as ‘cycling your tank’ is the process of ammonia being converted into nitrite and then nitrate. Bacteria feed on and turn harmful ammonia in to nitrites, and other bacteria feed on the nitrite and turn it in to nitrates. Once all of the ammonia and nitrite has been processed into nitrates, the tank has ‘cycled’ and a good colony of nitrifying bacteria has been built up. Fish waste, uneaten fish food and coral/fish decay can all add ammonia to the water column. Bacterial populations can increased and decrease in size based on the amount of ammonia added to the system. This is why it is important to add corals and fish gradually. The bacteria populations need time to catch up with the added ammonia from fish waste and feedings.
WHAT IS DRY LIVE ROCK?
Live rock is a term used interchangeably to describe rock that HAS beneficial bacteria living inside it and rock that HAD beneficial bacteria inside it. The key difference is that one is still wet, usually from an existing reef system, and the other has dried out. Dry live rock is any reef rock that has since dried out but had previously supported reef life. Dry live rock is often quarried from fossilized reefs or dead reefs. Dry live rock has significant advantages over live rock. Live rock has all the algae, critters and creatures from a reef in and on it, some good, some very bad. Dry live rock is totally pest free, no bad critters (commonly called hitchhikers) or pervasive algae to deal with. This can prevent difficulties later on as the system matures.
AVOIDING POTENTIAL PROBLEMS.
As we said at the outset, the type of live rock you choose will determine the needed steps to create a balanced and stable environment for your corals. In short, the way you setup your reef system with live rock (already wet and colonized with denitrifying bacteria) and the way you set it up with dry live rock (no bacteria at all) is very different.
Live rock from an existing reef system could potentially be put in a brand new reef tank and continue to thrive. Some of the denitrifying bacteria will be lost in the transfer from temperature, alkalinity, PH and other fluctuations or system differences. But corals, fish and inverts could gradually be added to the tank over the next few weeks, if not right away. However, you will also inherit any hitchhikers from the previous system, including pervasive and unsightly algae’s that could take advantage of your new systems imbalances and spread quickly. So if you plan to go this route, choose your live rock carefully. Try to get it from an existing system that is does not currently have pest or algae issues.
To avoid these potential problems, dry live rock is free of living pests and algae. However, it could contain dead pests and algae. These won’t spring to life when added to fresh saltwater, but they will continue to decay, creating ammonia and raising phosphate levels. This isn’t necessarily a bad thing at this point, so don’t panic. You need an ammonia source to get your cycle started. The amount of dead material on the dry live rock will determine, to a point, how long it takes your tank to fully cycle and process all of the ammonia. So some choose to clean or ‘cook’ the dry live rock first, in hopes that it will reduce the cycle time. This isn’t always necessary, but it can help shorten cycle time.
THE DIFFERENCE BETWEEN ‘COOKING’ & CURING LIVE ROCK.
The term ‘curing’ live rock is used interchangeably with the term ‘cycling’ your tank. Once live rock has cured or cycled, it has gone through the nitrogen cycle and is ready to support reef life. ‘Cooking’ your rock, however, refers to the removal of excess phosphate locked in the rock. A better term would be ‘de-phosphating’ your rock. This can happen before or after the rock has cured/cycled because the rock will continue to leach phosphate in the water column regardless of the bacteria colonizing it. There are several methods of ‘cooking’ your live rock, but all involve the aggressive removal of phosphates which are trapped in the surface layers of the rock.
One option is a Muriatic Acid bath. First the rock is soaked in a 10/1 ratio of fresh water and bleach. The bleach is thought to break down any organic compounds trapped in the rock. The rock is then left to dry out so that the bleach can evaporate, which usually takes about 24 hours. It is then submersed in a 15/1 ratio solution of fresh water and muriatic acid. The surface layers of calcium carbonate bubble and dissolve, releasing the trapped phosphate. Safety equipment must be worn during this process and the rock should be checked every 10 minutes or so to ensure that enough of the surface layer has dissolved. The remaining muriatic solution is then neutralized with baking soda and discarded.
The other option involves curing/cycling the rock in a container other than your display tank. The idea is to keep the container in darkness to avoid algae outbreaks and run phosphate removal media like GFO, Rowaphos or Lanthanum Chloride aggressively to reduce phosphate levels. Some choose to do large water changes as well during this process, but it’s easier to just run the phosphate removal media heavily until phosphate readings have reached acceptable levels and then start curing/cycling the rock.
SETTING UP YOUR ROCKSCAPE – WATER FLOW.
You should also consider what type of rockscape you want and how this will effect water flow in your tank. Low flow areas could be susceptible to algae and detritus build up. Busy rockscapes could require more powerheads or larger, more expensive powerheads to get adequate water flow throughout your tank. So some planning is needed. Avoid symmetrical rockscapes and rock walls as these will create issues with coral placement later on. Aim for an asymmetrical rockscape with high and low points angled diagonally across your tank as this will create the allusion of (front to back) depth. It will also add a new viewing dynamic to your tank as viewers discover new areas of the tank from different perspectives.