How to make your own live rock

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Alex Correa explains all about the purpose of live rock and offers a step-by-step guide to making your own artificial hard stuff...

The popularity of reef aquariums has been responsible for much global investment this past decade. Some ideas and systems have changed, but always stable is the concept of live rock, supporting, as it does, the beneficial bacteria that’s needed.

Natural or artificial, it represents the most important component of natural marine systems.

The live rock environment reveals an amazing interactive world and relationships between crab and coral can often be seen providing mutual protection against organisms from the rocky substrate.

Unfortunately live rocks are still collected from reefs which are under increasing threat. When removing a natural resource from any environment a natural or artificial replacement is needed — unless that resource won’t be harvested further.

As for live rocks, when we remove the material from the ocean the natural re-formation of any more could take at least three to five years — and that depends on many issues.

Rocky issues

We need to face some key questions. What exactly are live rocks and how much do we need them? Are we dependent on natural live rock harvests? What’s the difference between natural and artificial live rocks? Can we maintain a healthy reef tank with just artificial live rocks for any length of time? How do we make artificial live rock and what with?

Artificial live rocks have been recently introduced into the market and artificial live rock can be ‘seeded’ in the ocean.

In places like the Hawaiian islands, where I live, this is now the only way to legally keep an aquarium with live rock.

The nitrogen cycle

One of the most important factors in aquarium keeping is the nitrogen cycle. It determines the success of keeping organisms in closed systems for long periods without huge water changes.

The nitrogen cycle works with two distinct transformations — nitrification and denitrification — and are undertaken by many different types of bacteria.

Nitrification is completed in two parts. The first involves the transformation of ammonia to nitrite and the bacteria responsible are Nitrosomonas, Nitrosospira, Nitrosococcus and Nitrosolobus, among others. These are aerobic, meaning that they all need oxygen to survive.

The bacteria will colonise all suitable aerobic surfaces which water comes into contact with when there’s good flow.

The second part involves another group of bacteria responsible in converting nitrites and breaking them down into nitrates. The bacteria responsible are Nitrobacter, Nitrosospira, Nitrocystis, Nitrococcus and others.

Nitrites are toxic to some living organisms and enough of them can do serious damage to many in a closed system. They can inhibit oxygen uptake in a fish’s bloodstream but in a fully cycled aquarium are kept in check by the helpful bacteria.

Nitrates have less negative influence because they are less toxic than nitrites. Nitrates are also basic nutrients feeding algae that can attack invertebrates, like the corals. They should be kept under 5ppm to avoid water pollution and algae overgrowth.

This particular waste product of nitrification can be removed by denitrifying filters, protein skimmers, water changes or uptake by algae filtration.

The other cycle is denitrification. The many genus of denitrifying bacteria normally found in closed systems are Micrococcus, Pseudomonas, Denitrobacillus, Bacillus, among others.

These bacteria live in a low oxygen environment, as inside a porous live rock or in deeper layers of the sand bed.

The bacteria consume nitrates and convert it into nitrogen gas, which is released through water movement and aeration.

Once we get to understand the nitrogen cycle, we know the importance of live rocks in marine aquaria. They support the live bacteria to do that job for us.

Real versus fake

Natural live rock works more efficiently than any other media available because it supports a constant interchangeable system of micro-organisms. Artificial live rocks can be similar and mutual qualities can be achieved if certain steps are followed during the construction, curing and seeding.

So, what’s the difference between the natural live rocks and the artificial variety? Apart from composition, the main difference between home-made and natural reef rock is the diversity of organisms found on them. Such differences can also be apparent among natural live rocks from distinct areas.

Both types will support bacteria for the nitrogen cycle. The quality of the calcareous material used

and manner in which we make the artificial rock will determine the areas to be colonised by bacteria, among other organisms.

Basically, a porous structure will help the development of greater numbers of bacterial colonies.

Natural rocks will introduce undesirable organisms into the system, like Aiptasia spp. anemones, Mantis shrimps,

fire worms and others.

With artificial live rock we can have what we want!

Saltwater aquariums planned to become natural systems, with any alternative for natural filtration, do not depend on natural live rock. Natural systems are related to the type of natural filtration by bacteria and not dependent on natural structures from coral reefs. Any organism can be introduced to an artificial live rock structure.

Mantis shrimps, for example, are regularly introduced in aquariums with natural live rock. With artificial live rock you can avoid such dangerous organisms.

How to 'seed' the rocks

Your new artificial live rock will be ‘dead’ because as yet it contains no living organisms, so you need to put them in.

‘Seed’ it by putting it on a natural live rock so organisms can migrate. Then wait and see the changes over the next few months.

The rocks I make are not seeded with natural rocks, but with a selection of organisms applied to the concrete rocks. This way, undesirables are not introduced.

Introduction of the organisms depends on size and body structure. To apply hard corals use underwater epoxy cement. For soft corals and zoanthids use a ‘superglue’ gel, making sure the base of the organism is dry before application, then place underwater and quickly but gently press the polyp or colony to the desired rock.

You need to find the right crevice or hole for sponges — and avoid exposing them to the air, as they are very sensitive.

Excellent seed choices include worms, copepods, amphipods, algae-eating snails and sea cucumbers. Scraped coralline algae can be spread for a faster overgrowth and water movement can help it flourish.

Attractively coloured, coralline algae normally indicate that a system is mature. They can also be seeded to the system, even without natural live rocks. Just scrape from any hard structure and sprinkle over the rocks.

Amphipods are among organisms that can be introduced with artificial live rock and they help control undesirable algae.

Coralline algae need various types of elements and compounds in order to thrive. Many are introduced through water changes, but they need to be maintained to promote coralline algae growth and reproduction.

We add certain elements to try to help coralline algae, including iodine. Normally we use potassium iodide solution as iodine is needed by both algae and invertebrates, but an excess could be undesirable in closed systems.

Calcium helps and the best way to dose is via kalkwasser mix (calcium carbonate). Other additives include calcium chloride and calcium reactors (kalk or CO2).

Corals with hard skeletons and bivalves also use calcium. In systems without such invertebrates, calcium additions are often unnecessary for coralline algae growth.

If the calcium rate drops in any coralline algae-only system add small amounts. Levels in a reef tank should be at least 380 mg/l.

Strontium is important and, together with calcium and magnesium, can be added as strontium chloride. Strontium levels in ocean waters are normally between 8 to 10 mg/l.

Other additives

Magnesium won’t normally be needed. It is replaced with water changes in high enough rates for coralline algae and coral growth when natural water or quality artificial salt mix is used. The usefulness of other additives to help coralline algae is still speculative. Some include vitamins B1, B12 and C, trace elements and amino acids, but should be applied with caution.

Coralline algae prefer between 24-26°C/75-79°F and minimum alkalinity of 8 KH (2.9 meq/l).

The experimental system pictured above uses only artificial live rocks to maintain biological filtration and form the reef’s structure. This proves that calcareous materials and concrete are successful.

Artificial rocks need no maintenance. Once mature, presenting no danger with pH fluctuation in a saltwater environment, they will act as regular natural live rock.

How to set up for an artificial live rock tank

1. You’ll need coral sand, cement, buckets, a plastic tub, trowel, spray gun and water.

2. Start by mixing one part of cement to two or three parts of coral sand.

3. Add water and mix, making sure it’s not too wet. Next, get more coral sand and pour it into the tub to use as a mould.

4. Make a hole in the coral sand you’ve poured into your tub and add the cement/coral sand mix from the bucket. Start by mixing one part of cement to two or three parts of coral sand.

5. Make the holes on the rock, using sand between the concrete layers. You could also add salt to make the rock more porous.

6. Make a rough rock shape from the cement mix and then cover with more coral sand.

7. Spray with water immediately after finishing and spray again over the next 24 hours to make sure the mix is well bonded.

8. After 24-48 hours carefully remove the rock from the sand and rinse off the excess with water.

9. The calcium hydroxide in the cement will cause a high pH. Soak for up to 60 days, or until the pH has dropped to 8.3.

10. Scraped coraline algae can be spread over the structure for fast overgrowth. Water movement helps it grow.

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