PAR requirements vary by coral type. Soft coral and most LPS need 50-150 μmol. Most acropora SPS need 200-350 μmol. Demanding SPS like Acropora millepora and Acropora hyacinthus need 300-450 μmol. Anemones need 250-500 μmol depending on species.
PAR (Photosynthetically Active Radiation) is the measurement of light wavelengths corals use for photosynthesis. Measured in micromoles per second per square meter (μmol/m²/s, often abbreviated to "μmol"). PAR matters because corals build energy through their zooxanthellae algae symbionts - too little PAR and they starve, too much and they expel their zooxanthellae (bleaching).
| Coral type | PAR target | Placement |
|---|---|---|
| Soft coral (leathers, mushrooms, zoanthids) | 50-150 μmol | Bottom/middle |
| LPS general (euphyllia, acan, lobo, trachy) | 100-200 μmol | Middle/upper |
| Goniopora, blastomussa | 75-150 μmol | Lower-middle |
| Easy SPS (montipora, stylo, pocillopora) | 150-300 μmol | Upper-middle |
| Standard acropora (most species) | 200-350 μmol | Upper third |
| Demanding acropora (millepora, hyacinthus, tortuosa) | 300-450 μmol | Top of tank |
| Anemones (BTA, magnifica, gigantea) | 250-500 μmol | Top, anemone picks |
Borrow or buy a PAR meter (Apogee MQ-510 is the hobby standard at ~$500, or rent one from a local club). Take readings at the placement of every coral. Ramp lighting up over 4-8 weeks if your readings are above the target - corals adapt slowly and sudden increases bleach them.
Same PAR can produce very different color and growth depending on spectrum. Reef-spec lighting hits these wavelengths heavily: 420-460nm royal blue (drives photosynthesis + fluorescence), 380-420nm violet (UV-adjacent, color popping), 440nm blue, 500-550nm green/cyan (some pop, mostly visual), 600-660nm red (minimal benefit, mostly visual). Most reef LEDs (Radion, AI Hydra, Reef Brite) tune the channels properly out of the box. Avoid generic "white" LEDs sold as reef lights - they usually run too red and not enough royal blue.
Use the manufacturer's coverage chart from your fixture and depth-adjust by 30-40% per 6 inches of water column. Or borrow a PAR meter from a local reef club - most have one to rent at $20/week.
Probably yes - browning indicates the coral is producing more zooxanthellae to capture more light. Either increase PAR (raise the colony, raise fixture intensity, or move the coral up the rock) or accept that it's a brown-out colony at current placement.