Free reef tank tool
Coral Placement Calculator
Find a safer spot for your coral based on light, flow, reef tank zone, and nearby coral spacing.
Not sure what coral you have? Scan a photo with Coral Identifier first.
How the Coral Placement Calculator Works
Coral placement is a balancing act between light, water movement, aggression, growth form, and the coral's actual identity. This calculator compares your planned spot with typical starting ranges for common reef aquarium corals. It weighs light or estimated PAR most heavily, then flow and spacing, with tank zone used as a final context check. A good score does not mean perfect placement. It means the inputs look close to a reasonable starting point for the selected coral profile.
If you do not know PAR, the tool estimates it from lighting strength, tank height, and zone. That estimate is intentionally cautious because fixture mounting height, spectrum, lenses, water clarity, rock shadowing, and surface movement can change the real number. A PAR meter is still the better reference when placing high-light SPS or moving a stressed coral.
Coral Placement by Type: Soft, LPS, and SPS
Soft coral placement
Soft corals often tolerate a wider range than many stony corals, but they still respond to light and flow. Mushrooms commonly start lower in the tank with gentle flow. Zoanthids and many leathers often prefer moderate light and enough indirect movement to keep tissue clean. Fast spreaders such as Green Star Polyps are often easier to manage on isolated rock. Soft does not always mean harmless, so leave room for spreading colonies.
LPS coral placement
LPS placement usually benefits from moderate PAR, indirect flow, and conservative spacing. Torch, hammer, frogspawn, Favia, Favites, chalice, and similar corals can sting neighbors, sometimes after lights out when sweepers are more visible. A fleshy LPS that is blasted by a pump may retract or tear, while one placed too close to another aggressive coral can lose tissue at the contact edge. When unsure, start lower and give the coral more space.
SPS coral placement
SPS corals such as Acropora, Montipora, and Birdsnest generally need stronger light, high turbulent flow, and stable conditions. The calculator treats upper or middle rockwork as a more likely fit for these profiles, but placement still depends on acclimation history. A coral coming from low PAR can bleach if moved upward too quickly. Treat SPS results as a planning guide and make light changes gradually.
Light and PAR: Why Placement Changes by Tank Zone
PAR usually changes quickly from the sand bed to the upper rockwork. A coral placed near the top of a shallow tank under a strong fixture may receive several times more usable light than a coral sitting near the sand in a deeper tank. Rock ledges can also create shadows that the calculator cannot see. That is why the result labels estimated PAR as estimated and recommends measured PAR when accuracy matters.
Flow and Coral Health
Flow helps corals exchange gases, shed mucus, and keep detritus from settling on tissue. The right pattern is not just stronger or weaker. Many LPS corals prefer indirect movement that makes polyps sway without folding over. SPS corals often need stronger, irregular movement around branches. Strong direct blast is treated as a risk because it can irritate tissue even when the total flow in the tank is appropriate.
Coral Aggression and Spacing
Spacing is one of the easiest placement details to underestimate. Some corals look peaceful during the day but extend sweepers at night. Others spread by mat, plate outward, or shade corals below them as they grow. The calculator reduces spacing scores for aggressive and very aggressive profiles, and it is extra cautious when LPS corals are close to other LPS corals. More space is usually easier than rescuing damaged tissue later.
What If You Don't Know the Coral ID?
Coral ID changes the result because a torch coral, mushroom, Montipora, and chalice can all react very differently to the same spot. If the coral is unknown, use a moderate, easy-to-observe temporary placement with extra spacing. Then compare the coral to trusted references, browse the Coral Guides, check the Coral Database, or scan a photo with Coral Identifier to get likely matches before moving it into a more demanding zone.
Related coral identification resources
FAQ
Where should I place soft corals?
Many soft corals do well as a starting point in lower to middle rockwork with low to moderate PAR and indirect flow. Some, like mushrooms, often prefer lower light and gentler flow, while Green Star Polyps are usually safer on isolated rock because they can spread quickly.
Where should I place LPS corals?
Most common LPS corals are safer to start on the sand bed, lower rockwork, or middle rockwork with moderate PAR and indirect flow. Leave extra room around aggressive LPS because sweeper tentacles can reach farther at night than the coral appears during the day.
Where should I place SPS corals?
SPS corals usually need stronger light, high turbulent flow, and stable water conditions. Middle to upper rockwork is a common starting area, but avoid sudden PAR increases and verify the species or genus before moving a coral into a high-light zone.
How much space should I leave between corals?
Peaceful corals may only need a few inches, while aggressive LPS and many brain or chalice corals often need much more room. Use the calculator spacing as a conservative starting point, then observe nighttime sweepers, growth direction, and tissue contact.
What if I don't know what coral I have?
Use a conservative temporary placement with moderate light, indirect flow, and extra spacing. Coral Identifier can scan a photo and provide likely matches, but you should still verify the result with trusted reef references before making major care changes.
Is estimated PAR accurate?
No estimate replaces a PAR meter. The calculator's estimated PAR is only a rough planning aid based on light strength, tank height, and zone. Use measured PAR whenever possible, especially for SPS or stressed corals.
Should I move a coral immediately if the calculator says poor placement?
Not always. A poor result means the spot looks risky from the inputs, but sudden moves can also stress coral. If the coral is not in immediate danger, plan a lower-risk adjustment and observe its response before making more changes.
Coral Identifier
Unsure coral IDs make placement harder.
Coral Identifier gives likely coral matches from photos so you can compare the result, verify it with references, and make more careful placement decisions.