lighting

PAR

Photosynthetically Active Radiation

Definition

PAR (Photosynthetically Active Radiation) measures the amount of light in the 400-700 nm wavelength range available for photosynthesis. In reef tanks, PAR is the make-or-break parameter for coral and host-anemone health, expressed in micromoles per square meter per second (µmol/m²/s).

Practical use in aquariums

SPS coral and host anemones generally need 250-500+ PAR at the placement; LPS thrive at 100-250 PAR; soft corals tolerate 50-150 PAR. Measured with a quantum meter (Apogee MQ-510 or equivalent) - reef LEDs at the manufacturer-stated wattage do NOT guarantee target PAR; depth, water clarity, and reflector geometry all matter.

How PAR fits the bigger picture

Understanding PAR matters because it's connected to broader husbandry decisions: lighting drives photosynthesis, coloration, and growth - get it wrong and corals/anemones bleach or recess.

Browse the Fast Aquatics care library for full husbandry tutorials covering PAR in context.

Aquarium-keeping fundamentals

Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.

Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.

Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.

Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.

Species-appropriate husbandry: research adult size, territoriality, diet, and tankmate compatibility before purchase. Use our tank stocking calculator + compatibility guides.

Frequently asked questions

How long does an aquarium take to set up? 4-6 weeks for full cycling + first stocking. Use our cycle ETA calculator + how long does cycling take.

What's the best aquarium for beginners? 20-gallon long. Big enough for parameter stability, small enough for budget + space. See beginner picks.

Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.