Placement & Coral Warfare

Placement is where the lessons of the last two chapters — light and flow — meet a third force most beginners never see coming: corals fight. They are not passive decorations arranged for your eye; they are armed, competitive animals that sting, poison, and overgrow their neighbors in a slow war for space and light. Place them thoughtfully and your reef grows into harmony. Place them carelessly and you will watch expensive corals melt for reasons you cannot explain.

This chapter teaches you to place a coral for three things at once: the light it needs, the flow it needs, and the peace of everything around it.

Placement Is a Three-Body Problem

Every coral you add has to satisfy three constraints simultaneously:

1. Light zone. SPS up high near the fixture, LPS in the middle, softies low and shaded. Put a coral where its PAR needs are met.
2. Flow zone. Strong turbulent flow for SPS, gentle for softies and sand-dwellers, moderate for most LPS. Put a coral where the water motion suits it.
3. Peace zone. Enough clear space that neither this coral nor its neighbors can reach each other to fight.

The art is finding the spot that satisfies all three. A coral in perfect light but crushing flow will suffer; one in perfect light and flow but jammed against an aggressive neighbor will lose the war. Beginners optimize for light alone and get stung; experts hold all three in mind.

The Weapons Corals Use

Corals wage war through three mechanisms, and you should know each one.

Sweeper tentacles. Many LPS, especially Euphyllia like hammers and torches, extend long, translucent, heavily stinging tentacles — often at night — that reach several inches beyond the coral's daytime footprint. Anything they touch gets stung and killed. The daytime coral looks innocent; the nighttime coral is a reaching, armed predator.

Digestive filaments (mesenterial filaments). Some corals, many LPS among them, can extrude their gut filaments to externally digest a neighbor they contact. A coral touching another can literally melt the loser's tissue.

Allelopathy. This is the invisible one. Many corals, softies especially, release chemical compounds into the water that suppress or poison other corals — chemical warfare with no physical contact required. In a small tank, a large leather or a bed of certain softies can chemically hold back SPS on the far side of the glass. This is why heavy softie tanks and SPS tanks are hard to mix, and why running activated carbon and a skimmer to strip these compounds helps mixed reefs coexist.

Spacing for Sweepers and Growth

The defense against physical warfare is space, and the mistake is measuring today's space instead of tomorrow's. A frag the size of a coin will become a colony the size of a fist or a dinner plate, and its sweepers reach further as it grows. Place corals for the size they will be in a year, not the size they are in the bag.

Give aggressive LPS a generous buffer — several inches of clear water minimum around Euphyllia, more if a torch is involved. Related corals often tolerate each other, so two hammers may fuse peacefully while a hammer and a torch war, but do not gamble on it with valuable pieces. When you must mount corals near each other, remember that gravity and growth both change the geometry over time.

Mounting So You Can Adjust

Because growth changes everything, mount corals in a way that lets you adjust later. Glue frags to small plugs or rubble rather than directly to the main scape when you are still figuring out placement, so you can pick them up and move them without a crowbar. Use a dab of cyanoacrylate gel for small frags and a two-part epoxy putty for larger colonies or awkward angles. A coral fragging kit with glue, putty, and plugs is as much a placement tool as a propagation tool, because good placement is iterative — you will move corals as they grow and as you learn.

Flow tuning is part of placement too. A pump aimed to sweep across the aggressive-LPS zone at night can knock down sweeper tentacles before they reach a neighbor, and adjusting a wavemaker pump to change how water wraps the scape can create the calm pockets softies want and the strong lanes SPS want in the same tank. Placement, light, and flow are one problem wearing three hats.

A Placement Workflow for New Corals

When a new coral clears quarantine and dipping, place it like this:

1. Identify its class — softie, LPS, or SPS — and its light and flow needs.
2. Pick the zone that matches both, then check what already lives near that zone.
3. Measure the buffer. Is there room for this coral and its neighbors to grow and, if it is an aggressive LPS, to deploy sweepers without reaching anything?
4. Acclimate low and slow to your light, as the lighting chapter describes, before moving it to its final high spot.
5. Watch for a week. Corals reveal unhappiness through closure, deflation, or tissue recession. Adjust before you commit with strong glue.

This deliberate approach feels slow, and it is, and that is the point. A reef planned for growth stays beautiful; one crammed for instant impact tears itself apart over the following year.

Common Placement Mistakes

A handful of placement errors account for most of the coral loss beginners suffer, and every one is avoidable.

The first is placing for today's size. A frag glued into a tight gap looks fine until it triples in size and starts a war with its neighbors. Always leave room to grow.

The second is optimizing for light alone. A coral shoved into the perfect PAR but jammed against an aggressive LPS, or blasted by a powerhead, will lose regardless of how good the light is. Light, flow, and peace all have to be satisfied at once.

The third is placing aggressive spreaders on the main scape. Green star polyp, some mushrooms, and clove polyps will overtake everything if given a continuous rock path; isolate them on islands.

The fourth is ignoring the sand-versus-rock distinction. Plate corals and open brains belong on the sand, not perched on rock where they will fall, get injured, and be stung. Rock-dwellers wedged into the sand get buried and rot.

The fifth is trusting a loose placement to hold. Corals that are not secured slide, tumble in flow, and end up wedged against neighbors. Even a temporary spot should be stable.

And the sixth is never reassessing. Placement is not permanent; as corals grow, yesterday's safe arrangement becomes today's border war. Walk your tank periodically and move pieces before the fight starts rather than after. The reefers with the most harmonious tanks are the ones who quietly relocate a coral the moment they see a growth trajectory heading for trouble. None of these mistakes require expertise to avoid; they require only the discipline to place a coral for the reef it will become rather than the gap it fits today, and to keep watching as the scape fills in.

FAQ

How do I place corals so they don't fight?

Give each coral space to grow into and, for aggressive LPS like hammers and torches, several inches of clear water beyond their reach, because many extend long stinging sweeper tentacles at night. Place corals for the size they will be in a year, not their current size, and separate heavy soft-coral areas from SPS since softies release growth-suppressing chemicals into the water.

What is coral allelopathy?

Allelopathy is chemical warfare between corals: many species, especially soft corals, release compounds into the water that suppress or harm other corals without any physical contact. In a small tank this can hold back corals on the opposite side of the glass. Running activated carbon and a protein skimmer to strip these compounds, plus water changes, helps mixed reefs coexist.

Should I glue corals down permanently right away?

Not while you are still learning a coral's preferences. Mount new frags on small plugs or rubble so you can reposition them as you observe how they respond to light, flow, and neighbors. Once a coral has proven happy in a spot and begun to grow, you can commit it more permanently. Placement is iterative, because corals grow and change the geometry around them.