• 91 cm in one uninterrupted span - the largest arch CaribSea makes, and the only way to get this reach without bonding pieces together.
• Open swim-through for large fish - the point of a mega arch is that tangs, angels and wrasses use it as a corridor rather than swimming around a wall of rock.
• Aragonitic base rock, not cement - 97% calcium carbonate with trace strontium, magnesium and barium, so it behaves like reef rock rather than moulded concrete.
• Around 50% void space - interconnected micro and macro pores through the body of the piece, which is where the nitrifying bacteria live.
• Spored bacteria infused - AragAlive treatment gives a new system a biological head start.
• No curing and no die-off - dry rock with nothing collected on it, so there is no ammonia release and no weeks of curing before it can go in.
• Individually hand-made - CaribSea states dimensions and weight vary from piece to piece, so no two arches are alike.

Only length really decides this one. Our rule for a feature rock is that it should span no more than about half the tank's length, so water still moves around and behind it and the scape does not read as a single wall.

Front-to-back depth matters as much as length. An arch of this reach needs a tank around 60 cm deep before it can sit far enough off the back glass to clean behind, and enough water height above it that fish are not funnelled into the top few centimetres.

• One Life Rock Mega Arch, 36 inches (91 cm) long

Not included: base rock, aquarium sand, reef putty or cement, and any bacterial starter. This is a single piece sold on its own, not a boxed weight of assorted rock.

CaribSea does not publish a weight for the Mega Arch, and we will not put a number on a page we cannot source. The manufacturer's position is that these are hand-made products and both dimensions and weight vary between pieces.

What we can tell you is the shape of the answer. The XL Arch at 61 cm runs around 11 kg, and the Mega is half again as long with proportionally more mass at the shoulders. Plan on handling it as a genuinely heavy single object, with two people and clear access above the tank.

If the exact figure matters for a freight quote or a stand calculation, ask us before ordering and we will weigh the piece in stock.

A mega arch is the centrepiece of a large scape, never the whole of it. 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. Tanks in the size range this arch suits work out like this.

Many large modern reefs run well under these numbers on purpose, keeping open sand for flow and for placing corals later. Treat the table as the traditional ceiling rather than a target.

1. Dry-fit outside the tank first, on the floor, and decide the orientation before anything is wet. Turning this arch around inside a filled tank is not realistic.
2. Set it on the base glass, never on the sand bed. Sand settles and burrowing fish undermine it, and a piece of this mass shifting against a glass panel is a real risk.
3. Get two people on it and use a foam or eggcrate pad under the contact points to spread the load, particularly on acrylic or bare-bottom systems.
4. Confirm at least three solid contact points and no rocking before you fill. Shim with flat offcuts of base rock rather than relying on sand to level it.
5. Dress sand around the base afterwards, so the arch sits on glass and the sand only looks like it is holding it.

Life Rock is dry rock with bacteria added, not ocean-collected live rock. That is why no curing is required - there is no collected life on it to die off and release ammonia.

The spored bacteria shorten the cycle; they do not replace it. A new system still has to grow a bacterial population matched to its stocking, so dose ammonia or stock slowly and test until ammonia and nitrite both read zero.

Suitable for: large marine and reef aquariums from about 180 cm; fish-heavy systems where large swimmers need a corridor rather than a wall; show tanks built around a single architectural feature; and large hard-water freshwater displays such as Malawi and Tanganyika setups.

Not suitable for: tanks under about 150 cm, where a 91 cm arch dominates the scape and strangles end-to-end flow; planted, blackwater, shrimp and discus systems, since calcium carbonate raises pH and hardness; and anyone after the biodiversity of collected live rock. It is not a way to skip cycling a new tank either.

There is no maintenance schedule for the rock. In a marine tank the engineered coating is progressively overgrown by real coralline algae, usually inside the first year, after which the piece reads as established.

Blow detritus out from under the span at water changes with a powerhead or a large baster. A 91 cm overhang shelters a lot of dead water, and settled detritus under it is exactly what feeds nuisance algae in a big tank.

Coating chips from handling are cosmetic only. The aragonite underneath colours in once coralline establishes.

• CaribSea South Seas Base Rock 18kg - the plain bulk rock that fills out a large scape around the arch.
• CaribSea Life Rock Shelf Rock 18kg - flat plates for coral shelves either side, in the matching finish.
• CaribSea Life Rock Mega Cave 16" x 16" - the other oversize feature piece, if you want a cave to balance the arch.
• CaribSea Arag-Alive Fiji Pink - live aragonite sand to dress the base once the arch is seated.
• CaribSea Purple-Up - calcium and strontium supplement aimed at bringing coralline over the coating sooner.

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.

This is an oversize, fragile, single-piece item. The Australian distributor notes that because of the fragile nature of this rock, pieces can break in transit, and a 91 cm span is the most vulnerable shape CaribSea ships. Unpack and inspect before the delivery is signed off. Given the size and the freight involved, talk to us before ordering if you want it packed or transported a particular way.

How big is the CaribSea Life Rock Mega Arch?

It is 36 inches (91 cm) long and sold as a single arch. CaribSea does not publish a width, height or weight, because each piece is hand-made and those figures vary.

What size tank does the Mega Arch suit?

A 180 cm tank is the natural fit, where the arch spans about half the length. It works well in 210 cm and 240 cm tanks. At 150 cm it takes 61% of the length and only works if it is the sole structure. Below that, use the XL Arch 24" instead.

How much does it weigh?

CaribSea does not publish a weight and we will not guess one. For reference, the 61 cm XL Arch runs around 11 kg. Contact us before ordering if you need the exact figure and we will weigh the piece in stock.

Does it need curing?

No. CaribSea states no curing is required. It is dry rock with no collected marine life on it, so nothing dies off and the rock releases no ammonia. The aquarium itself still needs to be cycled before stocking.

Is one Mega Arch enough rock on its own?

No. In the tank sizes it suits, a traditional scape wants 54 to 120 kg of rock in total, so the arch is the feature and base rock makes up the bulk. Some large modern reefs run far less rock than that by design.

Will my arch look like the photograph?

No. Every Mega Arch is individually hand-shaped, so the profile, the thickness of the legs and the colour distribution all vary. The photograph shows the shape and finish rather than the specific piece you will receive.