SPS Color Guide
Parameters That Matter
Every parameter, light setting, and flow target that affects coral coloration — in one printable reference. Stop guessing, start dialing in.
Updated March 2026. Ranges based on natural seawater (NSW) values and reef keeping best practices.
SPS Color Guide: Parameters That Matter
ReefTanker.com — Updated March 2026
Water Chemistry Parameters
Parameters sorted by impact on coloration. Focus on the high-impact parameters first.
| Parameter | Ideal Range | Impact | Too Low | Too High |
|---|---|---|---|---|
| Nitrate (NO₃) | 2–10 ppm | High | Bleaching, starvation, tissue loss | Brown coloration from zooxanthellae overgrowth |
| Phosphate (PO₄) | 0.03–0.08 ppm | High | Bleaching, poor growth, skeletal thinning | Brown coloration, inhibits calcification |
| Alkalinity (dKH) | 7.5–9.0 dKH | High | Slow growth, weakened skeletons, susceptibility to STN | Tip burn on Acropora, tissue irritation |
| Calcium (Ca) | 420 ppm | Medium | Slow skeletal growth, thin branches | Can precipitate with alkalinity, causing instability |
| Magnesium (Mg) | 1350 ppm | Medium | Destabilizes calcium and alkalinity; indirect color loss | Generally well-tolerated up to 1500 ppm |
| Potassium (K) | 390–410 ppm | Medium | Linked to STN/RTN, reduced fluorescence | Generally safe up to 430 ppm |
| Salinity | 1.025–1.026 SG (35 ppt) | Medium | Osmotic stress, pale coloration | Osmotic stress, irritated tissue |
| Temperature | 77–79°F (25–26°C) | Medium | Slowed metabolism and growth | Bleaching, zooxanthellae expulsion above 82°F |
| Iron (Fe) | 0.01–0.05 ppb | Low–Medium | May reduce some pigment expression | Fuels nuisance algae; can harm invertebrates |
| Iodine (I) | 0.04–0.08 ppm | Low–Medium | Reduced soft tissue health, poor coloration in soft corals | Toxic at elevated levels; never dose without testing |
| Strontium (Sr) | 8–10 ppm | Low | Slightly reduced skeletal formation | Generally well-tolerated |
| Boron (B) | 4.5–5.5 ppm | Low | May affect skeletal integrity | Generally safe within range |
Parameter Notes
The single most impactful parameter for SPS color. Keep stable — gradual changes only.
Must stay in ratio with nitrate. Ideal NO₃:PO₄ ratio is roughly 100:1 (Redfield ratio).
Stability is more important than the exact number. Keep daily swings under ±0.5 dKH.
Consumed in tandem with alkalinity during calcification. Dose both in balance.
The hidden stabilizer. Fix magnesium first if Ca/Alk won't stay in range.
Often depleted in tanks with heavy SPS growth. Only measurable via ICP testing.
Use a refractometer calibrated with 35 ppt calibration fluid. Hydrometers are unreliable.
Stability matters. Daily swings over 2°F stress corals. Use a controller or reliable heater.
Extremely difficult to dose correctly. Only adjust if ICP shows deficiency. Less is more.
Important for soft corals and LPS. SPS are less dependent. Verify with ICP before dosing.
Usually maintained by water changes and salt mix. Rarely needs separate supplementation.
Maintained by water changes. Check via ICP if you suspect skeletal issues.
Lighting for Coloration
Spectrum and intensity settings that bring out the best color in SPS corals.
Spectrum
Blue and violet wavelengths (420–480nm) excite fluorescent proteins that produce vivid greens, oranges, and reds. White light washes out fluorescence.
PAR — Top of Tank
High-light SPS (Acropora, Montipora digitata, Stylophora) at the top need strong light to develop photoprotective pigments and full coloration.
PAR — Mid Tank
Most SPS and high-light LPS thrive here. Enough light for good color without bleaching risk.
PAR — Lower Tank
LPS, mushrooms, and shade-tolerant SPS. Lower light = more zooxanthellae = naturally darker coloration.
Photoperiod
Mimics natural reef lighting cycle. Ramping prevents light shock. Longer photoperiods increase algae risk without improving coral color.
Actinic Supplement
Extended blue period enhances fluorescent protein production without the algae-promoting effects of full-spectrum light.
Flow Targets by Coral Type
Proper flow keeps tissue clean, enhances gas exchange, and supports vibrant coloration.
| Coral Type | Flow Rate | Pattern | Notes |
|---|---|---|---|
| Acropora (branching) | 40–60x turnover | Strong, random/chaotic | Needs constant movement to prevent detritus settling and maintain color at tips |
| Montipora (plating) | 30–50x turnover | Moderate, alternating | Strong direct flow can damage thin plates; indirect turbulence is better |
| Stylophora / Pocillopora | 30–50x turnover | Strong, random | Hardy SPS that tolerate a wide range of flow; color responds well to increased movement |
| LPS (Euphyllia, Torch) | 15–30x turnover | Gentle, indirect | Too much flow causes tentacles to retract; look for gentle swaying motion |
| Chalice / Favites | 20–35x turnover | Moderate, indirect | Need enough flow to keep tissue clean but not so much it irritates the surface |
| Zoanthids / Mushrooms | 10–25x turnover | Low–moderate | Tolerate a range; very high flow causes them to close up and lose color |
Coloration Priority Order
When troubleshooting dull or brown corals, work through these in order. Each step builds on the previous one.
- 1 Nutrients — Get nitrate to 2–10 ppm and phosphate to 0.03–0.08 ppm. This fixes the majority of brown coral problems.
- 2 Lighting — Blue-dominant spectrum (70%+), appropriate PAR for placement. Measure with a PAR meter if possible.
- 3 Flow — Random, turbulent, species-appropriate. No detritus settling on tissue.
- 4 Stability — Rock-steady alkalinity (±0.5 dKH/day). Consistent temperature. Stable salinity.
- 5 Trace Elements — Verify with ICP testing. Only dose what's deficient. Never dose blindly.
- 6 Time — 6–12 weeks minimum for new frags. Don't move corals around. Patience pays.
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