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Acclimating Corals to New LED Lighting: PAR Ramping & Photoperiod Schedule
🔄 A slow, gradual light increase prevents coral bleaching and tissue loss — This guide provides week‑by‑week PAR ramping schedules, photoperiod adjustments, and signs of successful acclimation.
Why Do You Need to Acclimate Corals to New LED Lighting?
Sudden increase in PAR or spectrum change stresses zooxanthellae, causing them to produce reactive oxygen species. This leads to bleaching, tissue retraction, and sometimes death.
Corals adapt to specific light levels over time. When you upgrade from T5 to LED, or move a coral from a lower‑light tank to a higher‑PAR zone, the symbiotic algae (zooxanthellae) cannot immediately adjust. BRS studies show that a PAR increase of more than 50% overnight causes visible bleaching within 48 hours. LEDs also often have different spectral peaks (more blue/violet) than T5 or metal halide, requiring additional acclimation. Without a careful ramping schedule, even hardy corals can die.
🚨 Warning: Even if your new LED has lower overall wattage, its concentrated blue/violet light can deliver higher PUR (usable radiation) to corals, effectively increasing light stress.
What Is the Recommended PAR Ramping Schedule for New LEDs?
Start at 50% of target PAR for 1‑2 weeks. Increase by 10% every week thereafter over 4‑6 weeks. Monitor coral expansion and color daily.
For example, if your final target PAR for SPS is 300 µmol, begin with 150 PAR for the first 14 days. Week 3: 180 PAR, Week 4: 210 PAR, Week 5: 240 PAR, Week 6: 270 PAR, Week 7: 300 PAR. 2Hr Aquarist schedule. For LPS and soft corals, start at 40‑50% of target. Use a PAR meter to verify each step. If you see any polyp retraction, browning (too little light), or paling (too much), hold the current level for an extra week. Many LED fixtures (Radion, AI Prime) have built‑in acclimation modes that automatically increase intensity over a set period – use them.
📈 Sample 6‑week schedule (SPS target 300 PAR)
Week 1‑2: 150 PAR
Week 3: 180 PAR
Week 4: 210 PAR
Week 5: 240 PAR
Week 6: 270 PAR
Week 7: 300 PAR (maintain)
Week 3: 180 PAR
Week 4: 210 PAR
Week 5: 240 PAR
Week 6: 270 PAR
Week 7: 300 PAR (maintain)
How to Use Light Acclimation Mode on Popular LED Fixtures?
Ecotech Radion: set “acclimation” in Mobius, choose duration (4‑8 weeks) and start percentage. AI Prime: use “acclimation” slider in MyAI. Kessil: manual dial or schedule via Kessil Logic.
Radion’s acclimation mode gradually ramps from a set starting intensity (e.g., 50%) to full over a chosen period. AI Prime’s acclimation works similarly – you set start intensity and duration. For Kessil, you can manually reduce the color and intensity dials for two weeks, then increase them by one notch every 3‑4 days. Mobius guide. If your light lacks an acclimation mode, use a PAR meter and manually adjust intensity every week. Another method: raise the fixture high (e.g., 18″ above water) initially, then lower it by 1 inch every week until you reach desired height.
💡 Pro tip: Take a photo of your corals under white light before starting acclimation. Compare weekly to detect early signs of stress.
What Photoperiod Should You Use During Acclimation?
Keep photoperiod at 8‑10 hours total, but reduce peak intensity duration to 4‑6 hours initially. Use 2‑hour ramps (sunrise/sunset) to further ease transition.
Total light energy = intensity × duration. To reduce stress, you can also shorten the peak photoperiod. For the first two weeks, run full intensity (at 50% PAR) for only 4 hours, with 2‑hour ramps before and after. Then gradually increase peak duration by 30 minutes each week until you reach 8‑9 hours. Melev’s Reef method. This approach is especially helpful if your light is non‑dimmable but you can control timing. Do not exceed 10 hours total light, even after acclimation.
⏱️ Common mistake: Reducing intensity but keeping 12‑hour photoperiod can still cause bleaching. Manage total daily light integral (PAR × hours).
How to Acclimate Corals When Moving Them Between Tanks?
Place new corals on the sand bed (lowest PAR) for 1‑2 weeks, then move them up 3‑4 inches every week. Use egg crate or frag racks to slowly raise them.
When you buy a coral from a store or another hobbyist, it may have been under very different lighting (e.g., T5 at 150 PAR). Start it at 50‑70 PAR on your sand bed. After 2 weeks, move it to a mid‑level rack. After another 2 weeks, place it on its final rock. Reef2Reef discussion. For delicate SPS, use a dedicated acclimation box (clear container with holes) hanging in the upper water column but with partial shading. Always temperature‑acclimate and dip for pests before placing in your tank.
📦 Acclimation box methodPlace coral in a clear plastic container with holes, attach magnet to side of tank near top. After a week, open lid or remove box.
📏 Rack methodUse a frag rack at sand level, then raise rack every week by 2 inches until final placement.
What Are the Signs of Successful vs. Failed Acclimation?
Success: full polyp extension, good color (not too dark or too pale), and visible growth (new polyps, encrusting). Failure: bleaching, tissue retraction, brown slime, or closed polyps.
Monitor daily. Good signs: SPS polyps extend day and night, LPS polyps inflate fully, soft corals stand upright. Colors should be vibrant but not fluorescent white. Bad signs: Acropora turns white (bleaching) – lower PAR by 20% immediately. LPS shrinks and shows skeleton – move to lower light. Brown jelly disease or rapid tissue necrosis (RTN) can follow severe light shock. Advanced Aquarist symptoms. If you see any negative signs, go back to previous week’s intensity and hold for two weeks before trying again.
✅ Daily checklist: Polyp extension? Color stable? No tissue recession? If yes, continue schedule. If any “no”, pause for 5‑7 days.
Do Different Coral Types Need Different Acclimation Speeds?
Yes. SPS need the slowest acclimation (6‑8 weeks). LPS acclimate faster (4‑5 weeks). Soft corals can often handle 2‑4 weeks. NPS corals should never be exposed to high PAR.
SPS have high metabolic rates and are sensitive to light shock. Acclimate them over 8 weeks when changing light types. LPS are more forgiving; a 4‑week schedule works. Soft corals like zoanthids and mushrooms can often be placed directly under moderate LED if they come from similar lighting, but still acclimate for 2 weeks. NOAA guidelines. For any coral that was previously under metal halide or T5, expect a longer acclimation to LEDs because of the intense blue peak. Always err on the side of slower.
| Coral type | Recommended acclimation duration | PAR increase per week |
|---|---|---|
| SPS (Acropora, Montipora) | 8 weeks | 10‑15% |
| LPS (Euphyllia, Trachyphyllia) | 5‑6 weeks | 15‑20% |
| Soft corals (zoas, mushrooms) | 3‑4 weeks | 20‑25% |
How to Acclimate Corals to a Completely New Spectrum (e.g., T5 to LED)?
Start with LED at very low intensity (20‑30% of max) and run only blue channels for first week. Slowly add white and increase overall intensity over 8 weeks.
Many corals kept under T5 or metal halide are not used to the narrow, intense blue/violet peaks of LEDs. Start your LED with blue/royal blue channels at 20%, all other channels at 0%. For week 2, increase blue to 40%, add violet at 20%. Week 3: blue 60%, violet 40%, white 10%. Week 4: blue 80%, violet 60%, white 20%. Continue until you reach your target spectrum. Reef2Reef success stories. This “blue‑first” method reduces shock because zooxanthellae absorb blue efficiently but need time to adjust to higher intensity. Never switch abruptly from T5 to full LED power – that is a common cause of coral loss.
📚 Explore more reef acclimation guides:
← Main Lighting Guide (T1)
Reef Hub (T2)
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Coral PAR requirements
Bleaching prevention
Reef brand comparison
PAR measurement guide
