Life Rock Arch 12" 4pk

• Four 30 cm arches in one box - enough separate pieces to build a run of tunnels, or to stack into one taller structure with swim-throughs at two levels.
• Aragonitic base rock, not cement - CaribSea builds these on real aragonite rock, so the pH-neutral-to-alkaline behaviour and the surface texture match natural reef rock rather than moulded concrete.
• Around 50% void space - a network of micro and macro pores running through each piece, which is where the bacteria that process ammonia and nitrite actually live.
• Spored bacteria infused - CaribSea's AragAlive treatment seeds the rock, which shortens the cycle rather than removing it.
• No curing, no die-off - this is dry rock. There is no ocean-collected life on it to rot, so there is no ammonia spike from the rock itself and no weeks of curing in a bin.
• Coralline-look coating - engineered aragonite coatings in muted reef colours, which CaribSea states are safe if grazed by tangs, urchins or snails.
• 97% calcium carbonate - with minor and trace strontium, magnesium and barium, so it dissolves benignly rather than leaching anything unexpected.

• Four Life Rock arches, 12 inches (30 cm) long each
• Approximately 9 kg of rock in total

Not included: base rock to sit the arches on, aquarium sand, reef putty or cement to bond the structure, and any bacterial starter you may want to add alongside. Each arch is individually shaped, so the arches you receive will not be identical to the photograph or to each other.

A 30 cm arch is the smallest of the three Life Rock arch sizes and the only one sold in multiples. That makes it the flexible option: you can run all four across a long tank, or use two and keep the others for a later rescape.

Our rule of thumb for a feature rock is that it should span no more than about half the tank's length, so water can still move around and behind it. On that basis a single 30 cm arch sits comfortably in a tank from about 60 cm, and a row of two or three suits a 120 cm tank.

Also check height. An arch needs clearance above it for light and below it for fish, so a 30 cm arch wants roughly 40 cm of water depth to look like a swim-through rather than a shelf.

Arches are structure, not the whole aquascape. Most reef tanks pair shaped pieces like these with plain base rock. The widely used guideline, and the one CaribSea's own Life Rock listings quote, is 1 lb of rock per US gallon of display volume - about 0.12 kg per litre. For a fuller scape with more caves and overhangs, 1.5 to 2 lb per gallon is the usual step up.

Modern reef aquascaping often runs deliberately below these figures to keep open sand and better flow. Treat the table as the upper bound of what a traditional scape uses, not a target.

Life Rock is dry rock with bacteria added, not ocean-collected live rock. The practical difference cuts both ways and it is worth being clear about.

What you avoid: die-off. Collected live rock arrives carrying sponges, worms and algae, much of which dies in transit and releases ammonia, which is why it has to be cured for weeks before it goes into a display. None of that applies here.

What you still need to do: cycle the tank. The spored bacteria give the biological filter a head start, but a new system still has to build a population large enough for its stocking level. Add ammonia or a first fish slowly, and test until ammonia and nitrite both read zero before stocking properly.

1. Unpack over a towel. The arches are fragile in transit and the coating chips if a piece is dropped on a hard surface.
2. Dry-fit the structure outside the tank first. Arches are far easier to balance on a bench than under water.
3. Seat the arches on the base of the tank or on base rock, not on the sand bed. Sand shifts and burrowing fish undermine anything resting on it.
4. Bond joins with reef-safe cyanoacrylate gel and putty if you are stacking. A 9 kg structure that topples onto a glass base is an expensive lesson.
5. Add sand around the base afterwards, so the rock is sitting on glass and the sand is dressed around it.

Suitable for: marine fish-only and reef aquariums; new tanks being scaped from scratch; rescapes where you want more caves without buying more base rock; and African Rift Lake freshwater tanks, where the aragonite content works in your favour by holding pH and carbonate hardness up.

Not suitable for: planted aquariums, soft-water community tanks, blackwater and Amazonian biotopes, shrimp tanks and discus systems. This is calcium carbonate rock and it will raise pH and hardness. It is also not a substitute for cycling a new tank, and it is not the right choice if you specifically want the biodiversity that comes with collected live rock.

No maintenance schedule applies to the rock itself. Over the first year the engineered coating is gradually overgrown by real coralline algae in a marine tank, at which point the pieces stop looking manufactured.

Blow detritus out of the arch mouths with a turkey baster or powerhead at water changes. Enclosed shapes trap waste more than open rock does, and a tunnel full of detritus feeds nuisance algae.

If the coating chips during handling, the exposed aragonite underneath colours in on its own once coralline takes hold. It is cosmetic, not structural.

• CaribSea South Seas Base Rock 18kg - the plain rock that makes up the bulk of a scape, so the arches stay the feature rather than the filler.
• CaribSea Arag-Alive Fiji Pink - live aragonite sand to dress the base of the structure, from the same bacterial process.
• CaribSea Purple-Up - calcium and strontium supplement aimed at encouraging coralline algae to grow over the coating.
• Life Rock Arch XL 24" - the single large arch, if you want one dominant span rather than four smaller ones.

CaribSea does not publish a warranty term for Life Rock. Your rights under the Australian Consumer Law apply regardless and are not limited by anything the manufacturer does or does not offer.

The Australian distributor notes that because of the fragile nature of this rock, pieces can break in transit. Arches are the most breakage-prone shape in the Life Rock range, since the span is the weak point. A broken arch is still perfectly good rock and often makes two useful overhangs, but if you need the arch intact, unpack and check the box on arrival.

Does CaribSea Life Rock need to be cured before use?

No. CaribSea states no curing is required. It is dry rock with no collected marine life on it, so there is nothing to die off and no ammonia released by the rock. You still need to cycle the aquarium itself before stocking.

How many arches come in the box?

Four, each about 12 inches (30 cm) long, in a box weighing around 20 lb (9 kg). Every arch is individually shaped, so the four you receive will differ from each other and from the product photograph.

Is the purple coating safe if my fish pick at it?

CaribSea states the coating is safe if consumed by aquarium animals. Tangs, urchins and snails routinely graze it, and over time real coralline algae grows across it in a marine tank.

Can I use Life Rock arches in a freshwater tank?

Yes, in hard alkaline freshwater. The rock is 97% calcium carbonate, so it raises pH and carbonate hardness - useful in an African Rift Lake tank, wrong in a planted, blackwater or shrimp setup.

Do I still need base rock as well?

In most tanks, yes. At around 9 kg the box supplies a fraction of the rock a traditional scape uses, and arches are shaped as features rather than as bulk. Pair them with plain base rock and let the arches carry the structure.

Will the arches hold coral frags?

Yes. The porous aragonite surface takes reef-safe cyanoacrylate well, and the underside of an arch is a good spot for low-light species that would burn on an exposed high rock.