RecifAtHome guide
The giant clam is one of the most spectacular animals in a reef aquarium. Like corals, it hosts symbiotic algae in its mantle, making light its main energy source.
In short
- Start with Tridacna derasa or squamosa, the hardiest species.
- Provide strong lighting: PAR of 150 to 300 µmol/m²/s depending on the species.
- Calcium, alkalinity and magnesium must be stable: the clam builds a calcium carbonate shell.
- Inspect the shell on arrival: parasitic snails (pyramidellids) must be removed.
Giant clam species
| Species | Adult size | Light | Placement | Difficulty |
|---|---|---|---|---|
| Tridacna derasa | 50 cm | Medium to high | Sand | Easy |
| Tridacna squamosa | 40 cm | Medium to high | Sand or low rock | Easy |
| Tridacna maxima | 35 cm | High | Rock | Moderate |
| Tridacna crocea | 15 cm | Very high | Upper rockwork | Demanding |
Small giant clams under 5 cm are more delicate because they rely more on phytoplankton. For a first clam, choose a specimen of 6 to 10 cm.
Lighting and placement
Giant clams need strong lighting. Aim for roughly 150 to 200 µmol/m²/s PAR for derasa and squamosa, and 250 to 300 or more for maxima and crocea; a PAR meter helps you find the right spot. On arrival, place the clam lower than its intended final position, then move it up gradually over two to three weeks.
Sand-dwelling species (derasa, squamosa) should sit on the sand, on a small flat stone if the sand is fine. Crocea and maxima attach to rock using their byssal threads (beneath the hinge): never pull them free; if necessary, cut the threads with a clean blade.
Water parameters
| Parameter | Recommended value |
|---|---|
| Calcium | 400 to 450 mg/L |
| Alkalinity (KH) | 7 to 9 dKH |
| Magnesium | 1,250 to 1,400 mg/L |
| Nitrate | 2 to 10 mg/L |
| Phosphate | 0.03 to 0.1 mg/L |
| Temperature | 24 to 27 °C |
Water completely devoid of nitrate and phosphate is not ideal: the mantle fades and growth slows. Supplements of calcium and alkalinity must balance consumption, which increases with size.
Feeding
An adult giant clam gets most of its energy from light. Small specimens benefit from phytoplankton two to three times a week, with the pumps switched off for a few minutes.
Pests and tankmates to avoid
- Pyramidellid snails: tiny white snails that feed on the mantle at night. Inspect the shell and underside on arrival, brush them off, and check again with a torch in the evening.
- Some fish nip at the mantle: dwarf angelfish, butterflyfish, some triggerfish. Check before adding them.
- Opportunistic crabs and shrimp may attack a weakened clam.
Signs of a healthy clam
A healthy clam has a fully extended, colourful mantle, an open siphon and closes quickly when a shadow passes over it. A mantle that stays retracted for several days, a gaping shell or a mantle pulling away from the edge are warning signs.
Frequently asked questions
Which giant clam is best for beginners?
Tridacna derasa or Tridacna squamosa, around 6 to 10 cm. They are the hardiest and least demanding in terms of light.
What lighting does a giant clam need?
Strong reef lighting: about 150 to 200 µmol/m²/s PAR for derasa and squamosa, 250 to 300 or more for maxima and crocea.
Do giant clams need feeding?
Adults get most of their energy from light. Small clams benefit from phytoplankton two to three times a week.
Why won't my clam open?
The most common causes are pests (pyramidellids), a sudden lighting change, a fish nipping the mantle or unstable parameters. Inspect it at night with a torch.
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Guide written by the RecifAtHome team, coral aquaculture in Roche-lez-Beaupré (France) since 2010. Updated: October 2026.