Should You Use Cured Or Uncured Live Rock?

Live rock has become a widely used media for filtration. It is a natural way to filter and it deals, within reason, with the full [tag-self]nitrogen cycle[/tag-self]. It is suitable for all marine aquarium systems, and is usually very successful if the quality and quantity are correct. In addition, it is an excellent aquascaping material, lending itself very well to rock formations (well, that‘s not really surprising is it!).

Seems the thing to use then as far as filtration and aquascaping are concerned. Properly used there aren’t any real drawbacks. There is one drawback though, and that is cost. Most aquarists use rock that has already been cured, as it is more convenient (I hate to use the word ‘instant’ in a hobby where patience is so important) and just pay the premium.

Why the cost? As the media is rock, it is bulky and heavy, though the weight does vary. Therefore the air freight costs are high. Many an aquarist could be taken aback by the potential bill for sufficient quality live rock.

Is there any way to reduce this cost? An obvious way is to use a different filtration system, such as a canister or trickle filter. These are not as efficient in bio-filtration as live rock as far as the coverage of the nitrogen cycle is concerned. In addition of course, rock still has to be purchased to decorate the aquarium though it will be a lot cheaper.

There is a way to buy live rock that is notably cheaper, and that is to choose uncured live rock. Live rock is cured often by the retailer, and this time and effort, plus the equipment needed to achieve it, has to be paid for.

‘Cured’ live rock! What happens, is it injected with a special medication or something? No, it simply means that time is given for the life on the rock to die off, so that the aquarist can put the rock to nearly immediate use.

Live rock is collected from around the reefs, and consequently has all sorts of growths on it. These life forms have varying degrees of toughness, and a great many succumb to the rigours of transportation and changes of environment. Those that are left could add to the interest of the display aquarium (or not, depending on what they are!).

It is the loss of life that is of concern. It is well known that ammonia and nitrite are toxic to aquarium life and need to be avoided. As the dead life forms on and in the rock rot, and those that are dying eventually rot, toxics could reach high levels. This would be death to aquarium livestock. Therefore the rock needs to be given time in a suitable environment for this cycle to pass. Some life forms may die in the curing process because of the high toxicity.

The retailer will have tanks that are used purely for curing live rock. They will be fitted with efficient protein skimmers and the rocks will be covered with seawater. In addition there will be good circulation present, and the temperature will be maintained at an appropriate level. As time progresses, the ammonia and nitrite cycle will pass, though this period could be quite protracted. It is this that the retailer is watching for, testing to ensure that it is clear. The rocks are often then rinsed in clean heated seawater, checked and put up for sale. The rock is considered as cured.

So how does this assist the aquarist? There aren’t any additional aquariums (usually) for doing the curing process. There is only one place it can be done, and that is in the eventual display aquarium. So let’s look at that.

The aquarium is 2/3rds full of seawater, at the appropriate specific gravity (SG) and temperature. If the rock is going to eventually permanently stand on a supporting grid then this must have been completely organised before water goes in. The rock is not put into the aquarium in a decorative way, just put in. Before this, the rocks are carefully inspected for any obviously dead or dying and rotting life forms, which are removed as efficiently as possible. Some aquarists actually scrub the rock in warm seawater, but this may damage desirable life forms on the surface that might have survived. If scrubbing is done, a separate container is used – a large bucket or whatever – to keep scrubbed off items out of the main tank. As the rocks go into the aquarium, so the water will rise. If too much water is present, then it can be removed. If otherwise, it can be topped up.

Apart from heaters, the aquarium should be fitted with seawater circulators. These will be required when the display proper is ready so does not represent an additional expense. An efficient and appropriately sized protein skimmer should be switched on, again this will be required anyway. During the curing process, the protein skimmer should be regularly checked and cleaned when necessary (as when the display tank is properly functional) so that its efficiency is not reduced.

It will take time for the curing process, often counted in weeks. Any ’rubbish’ seen on the water surface or in the lower areas of the tank should be removed as far as possible, a fine net is useful for this. Also watch out for unwanted hitchhikers, such as crabs, mantis shrimps etc. though it is likely they will not be seen in the pile of rocks.

The aquarist should have three test kits available (again not an extra expense, they are required when the display tank is being stocked to monitor water quality). The kits are ammonia, nitrite, and nitrate. At first, after say three to five days, ammonia is checked. When this is detected, in the following period it is likely to rise. This can be monitored, and checks for nitrite commenced. It is not necessary to check every day, but when ammonia ceases to rise and begins to fall or disappears, nitrite checks can be done more regularly. Ammonia is at the front of the nitrogen cycle, and bacteria convert this to nitrite. Therefore if nitrite is present it shows that the initial bacteria battalions are at work. Nitrite may continue to rise, then start to fall or disappear. At this point check for nitrate, as this is the next to appear in the cycle. Nitrate could continue to rise to quite a high level, but should level out. This indicates that the nitrogen cycle is effective and has converted all toxins (ammonia and nitrite). Is this the end of the story? As far as the nitrogen cycle is concerned, the answer is no. Live rock is able, within reason and with time, to convert nitrate so that it can escape from the seawater as gas. It is best to let the nitrate fall a little, showing that nitrate conversion is in progress. The live rock is now nearly ready for use.

There should be available an amount of freshly mixed seawater, of the same SG and temperature as that in the tank. The amount should be equal to the largest volume that can be stored, say 20% or more of the tanks gallonage.

If necessary, lay a waterproof covering on the floor which is large enough to hold the live rock. The live rock can be piled up if necessary.

Remove each piece of live rock from the tank, giving it a rinse by moving it back and forward. If the following is going to take a little time, then the rocks can be covered in seawater dampened newspaper.

Siphon out some seawater, making sure that any debris is removed. Continue siphoning until the seawater removed is a little less than the new stored seawater. This can be done by measuring it out with a known volume bucket. This seawater is going to be thrown away, but keep the last bucket.

Now is the time to put in the decorative sand bed (pre-cleaned sand) if any. The live rock can now go back in, aquascaped as the aquarist desires. The water level will again rise, but be short once all the rocks are in. The new seawater can now go in. If the water level is a little low, use some from the bucket that was kept. Once at the desired level in the tank, all old seawater can be thrown away.

A check should be made that the heater(s), circulation devices and protein skimmer are in position and switched on.

The tank can be left for 24 hours, then the aquarist can do another ammonia, nitrite and nitrate test. Ammonia and nitrite should be undetectable. Nitrate is likely to be present. The guideline target for a reef tank is 10 ppm (parts per million) or less. If it is higher than this, the aquarist has two choices – wait and see if the bacteria in the live rock reduce it (this takes time) or do a further water change. The level above that desired will assist in the decision.

So the aquarist is now ready for stocking. One of the good things about curing is the high ammonia etc that is likely to arise, which means there is fuel for the bacteria – which means that the bio-filtration should be ready for livestock. However, this cannot be taken for granted and checks of ammonia and nitrite should be made as the display is slowly stocked. Nitrate needs to be monitored too.

It will be interesting as the age of the display increases to observe what life actually appears from the live rock. It could be various types of algae, small worms and the like. The aquarist will have introduced perhaps the best bio-filtration available, reduced the cost considerably, and, all things being equal, should end up with a wonderful marine display.