Coral Placement Guide: Where to Put Every Type of
Quick Summary
Coral placement is one of the most consequential decisions you make in a reef tank, and it is also one of the most forgiving to adjust. The core principle is vertical zoning: high-light, high-flow corals (SPS) go at the top of the rockwork, moderate-light corals (LPS) go in the middle, and low-light corals (soft corals, mushrooms) go at the bottom or in shaded areas. Beyond light and flow, you need to account for aggression spacing, growth projections, and the specific needs of each species.
Getting placement wrong does not kill corals instantly. It produces slow decline, retraction, color loss, or aggression damage that builds over weeks. The good news is that corals can be moved. If something is not thriving, repositioning it is almost always the first and best response.
The Vertical Zoning Principle
In every reef tank, light and flow create natural gradients from top to bottom. Understanding these gradients is the foundation of all coral placement.
Light Gradient
Light intensity drops significantly with depth. A fixture producing 400 PAR at the water surface may deliver only 150 PAR at mid-height and 50 to 75 PAR at the sand bed. This attenuation is your built-in zoning system.
The top third of your rockwork receives the highest PAR levels and is reserved for light-demanding corals. The middle third receives moderate light suitable for a wide range of species. The bottom third and sand bed receive the lowest light, which is perfect for shade-tolerant corals.
You do not need to measure PAR at every position to apply this principle (though a PAR meter helps if you have access to one). The general gradient holds true for virtually all reef lighting fixtures, and species placement follows the same pattern across different tanks.
Flow Gradient
Flow is strongest near powerhead and wavemaker outputs and weakest in sheltered areas behind rockwork. Unlike light, flow does not diminish predictably with depth. It follows the physical contours of your aquascape.
Corals that need strong flow go in exposed positions where water movement is unrestricted. Corals that need gentle flow go behind rockwork structures, in recesses, or in lower positions where turbulence has dissipated. Observing how water moves through your specific rockwork layout tells you more about flow placement than any general rule.
Placement by Coral Category
Each coral category has a target zone determined by its light, flow, and aggression characteristics. In most tanks, these zones overlap and blend rather than forming rigid boundaries.
SPS Corals: Upper Zone
SPS corals need the most light and strongest flow in the tank. Place them on the upper third of the rockwork, on exposed tops and ridges where PAR is highest and water movement is unobstructed.
Branching Acropora: Position on the highest points with the most light exposure (300 to 450 PAR). Leave space between colonies for growth. A 3 cm frag becomes a 15 cm colony within a year. Crowded Acropora colonies shade each other and engage in chemical warfare, causing tissue recession where branches contact or approach each other.
Plating Montipora: Can be placed on horizontal surfaces or ledges in the upper to mid zone (150 to 300 PAR). Plating species grow outward and need clearance above and beside them to spread without shading or being shaded.
Encrusting Montipora and Pocillopora: More flexible in placement than branching SPS. They tolerate moderate positions (150 to 250 PAR) and are good transitional corals between the SPS and LPS zones.
LPS Corals: Middle Zone
LPS corals occupy the middle of the rockwork where light has attenuated to moderate levels and flow is gentler.
Euphyllia (Torch, Hammer, Frogspawn): Place in moderate light (100 to 200 PAR) with gentle to moderate flow. Euphyllia tentacles sway best in indirect current. Direct powerhead blast causes permanent retraction. Leave 10 to 15 cm clear space around Euphyllia for sweeper tentacle reach.
Acanthastrea and Lobophyllia: Mid to lower rockwork, moderate to low light (75 to 150 PAR), gentle flow. These fleshy corals inflate significantly during the day and need space on their rock surface to expand without being pressed against neighbors.
Caulastrea (Candy Cane): Flexible in placement. Tolerates mid-zone conditions (100 to 200 PAR) and moderate flow. Peaceful enough to place near other non-aggressive species.
Duncan (Duncanopsammia): Mid-zone, moderate light (100 to 175 PAR), moderate flow. Duncans extend tall polyps and benefit from gentle current that allows full extension without flattening.
Soft Corals: Lower Zone and Shaded Areas
Soft corals generally go in the lower rockwork, shaded overhangs, and positions that would be too dim for stony corals.
Mushrooms (Discosoma, Rhodactis, Ricordea): Sand bed, lower rockwork, or shaded overhangs (30 to 100 PAR). Mushrooms placed too high bleach or retract. They spread naturally from their initial placement point, so position them where expansion will not interfere with other corals.
Zoanthids and Palythoa: Lower to mid rockwork (50 to 175 PAR). Zoanthids tolerate a wider light range than most soft corals and can bridge the gap between the soft coral and LPS zones.
Toadstool Leather (Sarcophyton): Mid-zone, moderate light (75 to 150 PAR), moderate flow. Toadstools grow large and produce potent allelopathic compounds. Place them away from sensitive stony corals and account for their eventual size (15 to 20 cm or more).
Xenia and Kenya Tree: Lower to mid rockwork, low light (50 to 125 PAR), gentle flow. Place on isolated rock that does not connect to the main structure if you want to control their invasive spreading.
Green Star Polyps: Versatile placement. Tolerates low to moderate light and moderate flow. Often placed deliberately on the back glass or overflow box as a living green backdrop.
Sand Bed Corals
Several coral species belong directly on the sand, not on the rockwork. Placing them on rock surfaces causes tissue abrasion and stress.
Trachyphyllia (Open Brain): Sand bed only. This coral inflates dramatically and needs soft substrate beneath its fleshy tissue. Placing Trachyphyllia on rock results in tissue tears as the flesh presses against hard edges. Low to moderate light (75 to 125 PAR), very gentle flow.
Fungia (Plate Coral): Sand bed. Free-living disc corals that sit on the sand without attaching. Moderate light (75 to 150 PAR), gentle flow. They can slowly move across the sand by inflating tissue and catching current.
Cynarina (Doughnut/Cat's Eye Coral): Sand bed or flat rock surface. Similar care to Trachyphyllia: low to moderate light, gentle flow, space to inflate.
Aggression and Spacing
Coral warfare is constant and invisible until you see its effects. Placing corals without accounting for aggression is one of the most common reasons for tissue damage in reef tanks.
Types of Coral Aggression
Sweeper tentacles. Elongated tentacles loaded with nematocysts, deployed at night to sting neighboring corals. Euphyllia, Galaxea, and some Favia species produce sweepers that extend 10 to 20 cm beyond their normal tissue footprint.
Mesenterial filaments. Digestive filaments extruded through the mouth or body wall to digest nearby coral tissue. Brain corals (Favia, Favites) and some LPS use this against corals that encroach on their space.
Terpenoid chemical warfare. Allelopathic compounds released into the water that inhibit or damage other corals at a distance. Leather corals (Sarcophyton, Sinularia) are the most potent producers. This aggression is not contact-based and affects corals throughout the tank.
Overgrowth. Fast-growing corals (GSP, Montipora, encrusting species) simply grow over slower neighbors, blocking light and smothering tissue. This is passive aggression but equally destructive.
Spacing Guidelines
When planning placement, these minimum distances prevent most aggression damage. Observe your corals at night periodically to verify sweeper tentacles are not reaching neighbors.
- Euphyllia to non-Euphyllia: 10 to 15 cm minimum
- Euphyllia to Euphyllia: Can be placed within 5 cm (same genus tolerance, with exceptions)
- Galaxea to anything: 15 to 20 cm minimum (exceptionally long sweepers)
- SPS to SPS (different species): 5 to 8 cm (chemical aggression at close range)
- Leather corals to SPS: Maximum practical distance, plus activated carbon
- Mushrooms to other corals: 5 to 10 cm (mild aggression through contact)
- Peaceful species (Duncan, Candy Cane, Blastomussa): Can be placed within 3 to 5 cm of each other
The Nighttime Inspection
Sweeper tentacles deploy 2 to 3 hours after lights-out. Using a red flashlight (which does not disturb coral behavior), check your tank at night periodically to observe how far tentacles extend. You will often notice sweepers reaching much further than expected, sometimes contacting corals that seemed safely spaced during the day.
If sweepers are reaching a neighbor, move one of the corals. Tissue damage from repeated nightly stinging shows up as white patches, tissue recession, or permanent retraction in the victim coral.
Planning for Growth
New reef keepers consistently underestimate how much their corals will grow. A well-placed frag today becomes a spacing problem in 6 to 12 months if growth was not anticipated.
Growth Rate Estimates
These approximate growth rates help you plan spacing at the time of initial placement.
- Acropora: 5 to 10 cm branch extension per year
- Montipora (plating): 5 to 10 cm radial expansion per year
- Pocillopora: 5 to 8 cm per year
- Euphyllia: 2 to 4 new heads per year
- Acanthastrea: 1 to 3 new polyps per year
- Duncan: 3 to 8 new polyps per year
- GSP: Can double coverage area in 2 to 3 months
- Zoanthid mats: 1 to 3 new polyps per week at mat margins
Spacing for Future Growth
Place frags with enough space around them to accommodate 1 to 2 years of growth before colonies contact each other. For fast growers (Acropora, GSP), this means leaving 10 to 15 cm of clear space. For slow growers (Acanthastrea, Blastomussa), 5 cm is usually sufficient.
In most tanks, the best approach is to start with fewer corals, well-spaced, and allow them to grow into a full display. A tank that looks sparse at 3 months looks spectacular at 12 months. A tank that looks full at 3 months becomes a warfare zone at 12 months as colonies grow into each other.
Acclimation After Placement
Every coral needs time to adjust to its new position, whether it is a new addition to the tank or an existing coral being moved.
New Coral Acclimation
Start all new corals in a lower-light, moderate-flow position regardless of their ultimate target zone. This allows recovery from shipping stress without the additional stress of maximum light intensity. After 1 to 2 weeks of observation (polyp extension, coloration looks normal, no tissue recession), begin moving the coral to its permanent position.
Move in small increments. Shift the coral 5 to 8 cm every 3 to 5 days, working gradually toward the target zone. This staged approach takes 2 to 3 weeks but dramatically reduces the risk of light shock or bleaching.
Moving Existing Corals
Corals that have been in one position for months have adapted their zooxanthellae density to that specific light level. Moving them abruptly to a significantly brighter or dimmer position triggers a readjustment period. The coral may retract, shed mucus, or temporarily lose color.
If you need to move a coral to a brighter location, follow the same graduated approach used for new additions. If moving to a dimmer location, the transition is less stressful and can be done in a single move.
Mounting Methods
How you attach corals to the rockwork affects their stability, health, and your ability to adjust placement later.
Superglue Gel (Cyanoacrylate)
The standard mounting method. Apply a dab of reef-safe superglue gel to the frag plug or coral base and press firmly against a dry rockwork surface for 10 to 20 seconds. The glue cures underwater but bonds best to dry surfaces, so drain or blot the bonding area if possible.
Superglue works for SPS frags, small LPS, zoanthid plugs, and any coral on a frag plug or small base. It provides a permanent bond that holds against moderate flow. For corals you may want to move later, use less glue so the bond can be broken with gentle force.
Epoxy
Two-part marine epoxy (such as Milliput or Aquaknead) provides a stronger structural bond than superglue and works on irregular, wet surfaces. Knead the two components together, press the coral base into the epoxy, and shape the epoxy against the rockwork.
Epoxy is ideal for mounting larger LPS colonies, leather corals with broad bases, and any coral that needs structural support on uneven rock. The downside is that epoxy is visible until it is overgrown by coralline algae (weeks to months), which affects the immediate aesthetic.
Frag Racks and Plugs
Temporary mounting on a frag rack allows you to test different positions before committing to a permanent placement. Frag racks hang on the tank wall or sit on rockwork ledges and hold multiple frag plugs.
Use frag racks during the acclimation period to find the ideal light and flow for each coral. Once you identify the best position, mount permanently with glue or epoxy. Frag racks are also useful for quarantine observation and grow-out before placing corals in the main display.
Natural Attachment
Many corals attach naturally to rockwork over time. Zoanthid mats, GSP, mushrooms, and encrusting Montipora will bond to adjacent surfaces within weeks if held in place long enough. Simply wedging a frag plug into a crevice or resting a coral against a stable rock surface allows natural attachment without adhesives.
Common Placement Mistakes
These errors are responsible for the majority of placement-related coral problems. All are correctable once identified.
Placing LPS in the SPS Zone
LPS placed at the top of the rockwork receive more light and flow than they need. The result is persistent polyp retraction, bleaching, and failure to thrive. If an LPS is not opening and your water parameters are fine, it is almost certainly placed too high. Move it down and observe.
Placing SPS in the LPS Zone
SPS placed too low receive insufficient light. They respond with slow growth, color loss (browning), and eventual tissue recession. If your SPS is browning despite good water chemistry, it likely needs more light. Move it upward gradually over 2 to 3 weeks.
Ignoring Sweeper Tentacle Reach
Corals that look safely spaced during the day can be in active warfare at night. Euphyllia and Galaxea sweepers extend dramatically after lights-out. If a coral next to an aggressive species is mysteriously declining, check for sweeper contact at night.
Crowding at Initial Placement
Filling every available rock surface with frags leaves no room for growth. Within months, colonies begin competing, shading, and stinging each other. Start sparse. The tank fills in naturally and looks better for it.
Placing Corals in Dead Zones
Dead zones (areas with minimal water movement) accumulate detritus on coral surfaces, reduce gas exchange, and promote bacterial growth. If a coral consistently collects visible debris on its tissue, the flow at that position is insufficient. Move the coral or redirect nearby flow.
Placing Sand Bed Corals on Rockwork
Trachyphyllia, Fungia, and Cynarina belong on the sand. Their inflated tissue abrades against rock edges and causes tissue damage. If you see a Trachyphyllia with persistent tissue damage on one side, it is likely contacting a hard surface when fully inflated.
Advanced: Reading Coral Behavior for Placement Feedback
Corals communicate their comfort with their position through consistent behavioral signals. Learning to read these signals allows you to fine-tune placement without relying solely on PAR meters or general guidelines.
Signs of Good Placement
- Full polyp extension during the day (SPS, LPS, and soft corals)
- Visible growth at tips or margins (new white growth tips on SPS, new polyp buds on LPS)
- Vibrant coloration consistent with the species' known palette
- Feeding response when food is present (LPS extending tentacles)
- Natural tissue inflation (LPS and soft corals filling out well beyond the skeleton)
Signs of Poor Placement
- Persistent polyp retraction (more than 2 to 3 days without other cause)
- Color loss: bleaching (too much light) or browning (too little light)
- One-sided growth or coloration (indicates uneven light or flow exposure)
- Tissue recession from one area (possible aggression from a neighbor or localized flow issue)
- Mucus production without the normal shedding cycle (stress response in leathers and some LPS)
When you see negative signals, change one variable at a time. Move the coral slightly (5 to 8 cm) and observe for 5 to 7 days. If the behavior improves, the new position is better. If not, try another adjustment. Patience and incremental changes produce better results than drastic repositioning.
Common Myths
"There is one perfect spot for each coral." Most corals thrive across a range of positions. The difference between a good spot and a great spot is subtle. Do not agonize over finding the single perfect placement. Find a reasonable position, observe, and adjust if needed.
"You should never move a coral once it is placed." Moving corals is a normal part of reef keeping. Corals adapt to new positions within 1 to 2 weeks. Gradual moves (small distances every few days) minimize stress. Leaving a coral in a poor position is far worse than the temporary stress of moving it.
"PAR is the only thing that matters for placement." Light is critical but so are flow, aggression spacing, and growth room. A position with perfect PAR but direct powerhead blast will stress most LPS. A position with ideal light and flow but within sweeper tentacle range of a Galaxea will result in tissue damage. All factors must be considered together.
"Corals at the bottom of the tank are not getting enough light." Many species thrive at low PAR. Mushrooms, Blastomussa, and Trachyphyllia perform best in the bottom third of the tank where light is dimmest. Placing them higher actually harms them. The bottom of the tank is not a compromise position. It is the correct position for shade-loving species.
FAQ
How do I know if my coral needs more or less light?
Bleaching or retraction indicates too much light. Browning or slow growth indicates too little. Move the coral 5 to 8 cm in the appropriate direction and observe for a week. Gradual adjustments are safer than large moves.
Can I place different Euphyllia species next to each other?
Generally yes. Euphyllia species (Torch, Hammer, Frogspawn) are usually tolerant of each other and can be placed within 5 cm. However, some individual colonies do sting other Euphyllia. Observe for 48 hours after placing them near each other and separate if you see tissue damage.
How long should I wait before moving a new coral to its permanent spot?
Allow 1 to 2 weeks in a lower-light acclimation position. Once the coral shows normal polyp extension and no signs of stress, begin moving it to the target zone in increments of 5 to 8 cm every 3 to 5 days.
Should I glue every coral to the rockwork?
Not necessarily. Frags that you are still testing for position can sit on ledges or in crevices without glue. Permanent residents benefit from secure mounting (glue or epoxy) to prevent them from falling during maintenance or being knocked by fish. Sand bed corals should never be glued. They sit freely on the substrate.
How far apart should I space coral frags?
For fast-growing SPS, leave 10 to 15 cm between frags. For moderate-growing LPS, 8 to 10 cm. For slow-growing species (Acanthastrea, Blastomussa), 5 cm is sufficient. Always account for 1 to 2 years of growth when choosing spacing.
What do I do if two corals are fighting?
Move the more mobile or less established coral. If both are permanently mounted, identify which is the aggressor (usually the one with visible sweeper tentacles or the one showing no damage) and move the victim to a position outside the aggressor's reach. Check at night to confirm the new spacing is adequate.