Short answer
SPS (small-polyp stony) coral has small polyps over a calcium-carbonate skeleton (acropora, montipora, stylophora). LPS (large-polyp stony) coral has large fleshy polyps over a heavier skeleton (euphyllia, goniopora, acanthastrea, lobophyllia). SPS demands stable parameters, intense light, and high flow. LPS is more parameter-tolerant, needs moderate light and flow, and benefits from feeding.
In depth
The SPS/LPS distinction is the central organizing principle of stony coral keeping. The "small" vs "large" refers to polyp size relative to the skeleton, but the practical implications run far deeper than visual differences.
SPS characteristics
- Small polyps (1-5mm typically) covering a continuous calcium-carbonate skeleton
- Branching, plating, encrusting, or table growth forms
- Intense light requirements (200-450 PAR depending on species)
- High flow requirements (20-60x tank turnover, turbulent rather than laminar)
- Photoautotrophic - derives 80%+ of energy from photosynthesis via zooxanthellae
- Demands rock-stable alkalinity (within 0.3 dKH), calcium (within 20 ppm), magnesium (within 50 ppm)
- Examples: acropora, montipora, stylophora, pocillopora, seriatopora
LPS characteristics
- Large polyps (1-10cm) covering a heavier, more visible skeleton
- Fleshy tissue extending dramatically when healthy
- Moderate light requirements (100-200 PAR)
- Moderate flow (10-20x turnover, no direct laminar flow on polyps)
- Mixotrophic - photosynthesizes for energy AND captures food particles for growth
- Tolerates wider parameter swings than SPS
- Examples: euphyllia (hammer, torch, frogspawn), goniopora, acanthastrea, lobophyllia, trachyphyllia, catalaphyllia, plerogyra
More questions
Can I keep SPS and LPS together?
Yes, in a mixed reef. The SPS goes in the upper third (high light, high flow), LPS in the middle to lower third (moderate light, gentle flow). Most modern reef tanks run mixed reefs successfully.
Which is harder to keep?
SPS, by a significant margin. SPS demands stable parameters that LPS forgives. Most beginners should build a soft-coral and LPS reef for 12+ months before adding SPS.