In todays environmental climate there is increasing pressure on Governments by environmental groups across the world to restrict the collection of anything and every-thing living for use in our aquariums.

Live rock seems to be the first prime target as in recent years the collection of live rock from Florida has ceased except for live rock leases.

It can also be seem in Hawaii where live rock collection was ceased many years ago.

Governments are currently working on restricting fish and coral collections within Australia and this trend is being following all around the world.

For these reasons alternatives to live rock are of vital importance and in years to come may possibly become the only cost effective alternative.

As limestone is mined from ancient coral reefs it has basically the same structure and composition as the live rock we use today.

For this reason it seems to stay relatively inert and is therefore ideally suited as a substitute for live rock in our aquariums.

LIME STONE - BENEFITS & DISADVANTAGES

Benefits

* Dense - being derived from the old coral reefs it has the same porous structure as live rock but is consistent and has no large cavities, etc. within.

* Extremely Cheap - Costs vary from country to country.

Here in Australia limestone rock can be obtained for approx. AUD$7.00 for a block of approx. 2.5ft. x 1ft. x 6inches.

This equates to approx. 10+ kilo.

Alternatively live rock has a value of between AUD$120.00 to $160.00 per 15-20 kilo.

* Malleable - can be shaped to any desired form e.g. size of tank, cavities for caves, rock shelves etc.

Limestone is easy to carve and can produce desired results such as vertical walls with overhangs; caves in the position and size to suit personal requirements.

In the case of caves it is possible to create solid walls with no light penetration as is the case with live rock due to the imperfect shape of individual pieces.

It is also possible to purchase large chips of limestone which can be as large as 1ft. x 1ft. and only 1-2 inches thick that are perfect for creating rock shelves or ledges.

* Because limestone is mined and does not come from a watery environment there a no parasites such as mantis shrimps, crabs, fireworms etc.

For this reason it can make an ideal substrate medium and aquarist paranoid about mantis shrimps and crabs.

Disadvantages

* Generally only supplied in square block form.

* No life whatsoever although this is rapidly overcome with the seeding of a little live rock.

* Large pieces may be too dense and therefore have relatively low surface areas for colonization of bacteria so vital to the longevity of our aquariums.

LIVE ROCK - BENEFITS & DISADVANTAGES

Benefits

* The major benefit of using live rock is the fact that there is an expansive amount of life from tiny Tubeworms to Star fish, sea urchins & the occasional fish.

This is ultimately what a real coral reef is made of and therefore is comes as close to us constructing a true representation of a coral reef in our aquariums.

* Provides seeding of various organisms that are a must for use with limestone as is contains none of these organisms itself.

These include algaes that make our tanks so appealing.

* Live rock also has an appeal to first time aquarists as at first glance it has many varieties of coral and is usually also red in colour.

Disadvantages

* Importation of nasty critters like mantis shrimps and crabs.

* Very restricted in shape and therefore ability to build aquaschemes.

* Sold by weight and therefore can be very expensive to purchase.

* Transport times can be extensive and therefore the potential of high mortality rate of organisms has a direct effect on ammonia spikes and high nutrients levels in our aquariums.

TIME TO NATURALIZATION & INTEGRATION

After 3.5 months the limestone that is in high light zones is now covered with red & purple coralline algae.

Organisms which are present on the live rock used to seed the system rapidly migrate to cavities upon the limestone.

No doubt anyone who keeps a reef tank will have found that tube worms rapidly multiply in coral sand and also spread all over uncleaned glass surfaces as does corralline algae which constantly grows across the front window of the aquarium.

METHOD:

1. The first step was to carve the limestone with channels and ledges and to also create a large cave.

This was then placed at the end of a 5ft. x 20in. x 20in. tank.

It sits on the top of the plenum with no coral sand beneath.

The corral sand covers only the plenum and the lower section of live rock (to the depth of the sand).

With no artistic flair whatsoever the writer believes that the structure for a first attempt looks very natural and is certainly better than most live rock aquascaped tanks.

The cave mentioned is located at the front of the tank and is basically just a 10in. long cavity viewed through the front glass.

At the origin of the cave there is an outlet for a power head.

The pump is placed in a cavity at the surface and constantly pumps water through the cave.

Thereby creating a current that passes by a yellow and an orange Tubastrea Coral.

This facilitates a convenient form of feeding the coral as all that is required is to place frozen food at the inlet of the pump.

2. By approx the end of the first month the high light areas of the limestone surface were covered by a brown algae, perhaps a diatom growth.

There was approx. (6) small spots of purple coraline algae beginning to grow and many spots of red coraline algae.

The system being used for calcium addition is an automatic top-up unit flowing through a magnetically stirred calcium hydroxide unit as per description in "The Reef Aquarium" by J.Charles Delbeek & Julian Sprung and also "The Modern Coral Reef Aquarium" by Svein A. Fossao & Alf Jacob Nilsen.

3. At approx. (2) months red coralline algae has 50% covered highly lit surfaces and purple coralline algae is noticeably prevalent.

Brown algae is now populating lower light areas with a light covering.

4. At (3) months there is the beginning of a population of small tube worms on the glass inside the cave so therefore I would assume that they are also populating the inner surfaces of the cave.

There is currently no algae whatsoever inhabiting this cave.

The lit surfaces are now 70% covered with coralline algae and the shaded surfaces are starting to grow purple and red coralline algae.

5. Today there is only slight growth of the various coralline algae as was on the third month.

Due to the fact that the limestone is carved and not assembled, as the live rock requires, it is possible to create solid caves.

These lend themselves perfectly to use, as I have with Tubastrea or other night loving corals, as it also creates defined flow paths for water and can be easily carved and drilled for ease of plumbing and pump placement.

In my opinion it is also an ideal medium to create "gorge tanks" as described in "The Modern Coral Reef Aquarium".

As they lend themselves to ease of constructing vertical walls with large overhangs that are technically impossible with live rock except when using various fastening methods such as fishing line and cable ties.

For this reason limestone can be used to create vertical walls that complement a live rock structure and to add an extra feeling of depth to a tank.

Other possibilities include:

* Construction of caves inside blocks that are adjoining the glass face of the tank thereby creating a small viewing area inside the cave where it is possible to see activity that you may not otherwise be able to see from the normal view of the tank.

* Waste limestone "chips" can be used as a medium to place small fragments of coral.

* As base structure of the main reef with the addition of live rock placed over the limestone.

OK, thats is it people. Hope this has been informative. Now for some questions.

Q: I've been told that limestone has a stabilized pH of 7.6 which might upset the pH of a tank. True?

The aqurium has been running for 6 months, with various bubble anemones, spawning colony of cleaner shrimp, clown fish, other anemones .....

Acropora sp., all growing and triving nicely as well as, two pairs of spawning Banggai Cardinals, and now juvenile Cardinals

If you add limestone to distilled water, and even some live rock (dead or otherwise) will take it to pH of 7.6, it is all the buffers etc in the seawater that maintain it at above 8.0. Chris

Q: In central Texas limestone can be had in natural shapes with many open pores, but these are usually lined with small brownish crystals. Are these a potential trouble source?

Sorry, but I don't know what these crystals are, and I live in Victoria Melbourne. You would have to find out what they are, then find out if that substance is harmful to marine life. Chris

garnet or quartz :-)

Well, if it is quartz, then that is silicon, and will dissolve into the water at around 12ppm, this your diatoms would love if silicon is the limiting nutrient. The rock that I use comes from Mount Gambier here in Australia, and appears to have no contaimination at all. Chris

Q: chris do you know of any sources of crushed limestone (pref graded) suitable for aquariums and available in nsw australia?

I don't currently know of any, but I can soon find out for you. The source that I have used typcially supplies limestone blocks for housing. Chris.

Q: Is there anything that can be leeched into the tank from the limestone?

Limestone is just ancient marine skeleton etc, i.e old reef. You can see the old urchin shells, fish, etc through out it. So what ever is part of a coral skeleton has the possiblity of leaching out. Chris.

Q: What water parameters would be useful to monitor (obviously silica based on what you just said) FeS is a potential pollutant but I dont know how to test for it.

Iron test kit for the FeS, this will tell you how much iron is in the tank ......

silicates could be a possibility as can phosphate, as it does with some grades of coral sand. Chris.

Q: how do you clean or sterilize your limestone?

I carved it, then washed it with fresh tap water to remove all the dust generated during the carving process. That is all you have to do. Chris

Q: can you convert the price per kilo to US dollars and lbs?

OK, US$0.53 per kg, US$0.25 per lb. Chris.

Q: can you make sand out of limestone for a live sand bed?

You could, but it would never be consistant, and a heap of dust would be generate. Chis.

Q: any tips on identifying the rock as limestone? What else can it be confused with?

Looks very similar to the surface of dead live rock, has many small pours that are easily seem. It has a slight yellow tinge, and has fossilised sea urchins, scallop shells etc in it. It is also fairly soft. Chris.

Q: What did you use to carve the limestone?

A standard masonry chisel and hammer. And can also be drill easily with a standard masonry drill bit and drill. And the wasted chips can the be used for mounting coral fragments. Chris

Q: Back to the 7.6 pH for a second, do you find yourself battling this issue any more than in an all live rock tank?

I have never touched pH in 4 years of keeping marine reef tanks, and this tank is no different. Chris.

Q: Is the use of a plenum suggested/required when using limestone, and if so, why?

No it is not, can be used in any type of reef tank. Even as a substitute for live rock, in the same shape as live rocks. Chris.

Q: Where do you find limestone for purchase?

Any supplier of limestone blocks for building houses etc. I looked it up in the Yellow Pages. Chris.

Q: Can limestone that is used for driveways that you buy from a shell yard be used?

I presume so, but I have not come across this source. Would depend on the purity, quality etc and I suspect that anything you use for a drive way would be harder, so it may be different. Chris

Thanks Chris!