# Why Are My Corals Dying? | Gulf Coast Aquatics

> Parameter swings, lighting issues, pests, flow problems — the real reasons corals die and how to diagnose what

URL: https://gulfcoastaquatics.locuspilot.com/guide/why-are-my-corals-dying/
Last-Modified: 2026-05-17

# Why Are My Corals Dying? The Most Common Causes

Parameter swings, lighting issues, pests, flow problems — the real reasons corals die and how to diagnose what's wrong.

![Bleached SPS coral next to a healthy coloured coral](/images/misc/bleached-white-sps-coral-next-to-healthy-colored-c.webp)

We frequently hear customers asking why my corals are dying, but it is rarely a single massive disaster that causes the problem. This compounding chain of small stressors usually separates a thriving reef from a struggling one — whether you bought your frags from us or another source, the 

corals and reef livestock

[/corals-reef-livestock/ →](/corals-reef-livestock/)

 we sell only thrive in stable systems. The good news is that most failures trace back to just four root causes.

Our team will walk you through these four common culprits and exactly what to check for each. You can review the data and explore a few practical ways to respond.

For free in-store water testing and a proper diagnosis, you can 

come in

[/contact/ →](/contact/)

 with a one-cup water sample any time the shop is open.

## Cause 1: Parameter swings

### Core Chemistry Swings

We find that unstable water chemistry is the most common coral killer for tanks past the beginner stage. Parameter swings trigger severe stress responses in your reef. Consistent levels matter much more than hitting textbook perfect numbers.

Our technicians constantly see the damage caused by these four rapid fluctuations:

-   Alkalinity swings that drop more than 0.5 dKH in a single day
-   Salinity drift from topping off with saltwater instead of fresh
-   Temperature spikes from broken heaters or AC cycles
-   Sustained pH drops below 7.8 that stress the coral skeletons

Alkalinity swings are highly destructive because SPS corals can suffer rapid tissue necrosis. Salinity drift occurs when evaporation concentrates the salt over several weeks.

### Managing Temperature and pH

We always warn hobbyists that a 2026 survey of US reef clubs showed heater failures cause 40 percent of temperature crashes. You should aim for less than a one-degree Fahrenheit daily temperature shift. Sustained pH drift below 7.8 severely stresses calcifying corals and slows their growth.

> Our service calls often reveal common signs of these parameter issues. You will likely see coral bleaching at the SPS tips where white tissue eventually grows back to color. The sudden appearance of LPS tissue recession or rapid coral browning also points to chemistry problems.

We recommend you stabilize your additions using a consistent schedule, so check out this guide on 

dosing for beginner reefers

[/guide/dosing-for-beginner-reefers/ →](/guide/dosing-for-beginner-reefers/)

. This simple upgrade prevents human error and keeps salinity rock solid when you automate your freshwater top off. You must also verify that your primary heater works by checking it against a secondary backup thermometer.

## Cause 2: Lighting wrong

### Visual Signs of Bad Lighting

Our lighting assessments show that incorrect illumination will cause corals to brown out, recede, or starve. If the light is too intense, corals expel their zooxanthellae and bleach completely white. The wrong spectrum simply prevents them from growing at a normal rate.

We look for specific visual indicators to diagnose lighting issues in customer tanks. Signs of too little light include corals turning dark brown as zooxanthellae increase to compensate, tissue receding, and polyps staying closed. Signs of too much light include pale or stark white bleaching, rapid tissue necrosis, and tightly retracted polyps.

Our clients often notice signs of the wrong spectrum when corals look pale or muddy under their home fixtures compared to the shop display.

![Hand pointing at receding coral tissue base](/images/misc/hand-pointing-at-receding-coral-tissue-base-under-.webp)

### Measuring and Fixing PAR

The best fix is to take a Photosynthetically Active Radiation measurement directly at the coral level using an industry-standard tool like the Apogee MQ-510. Most modern reefs thrive within specific target ranges based on the coral type.

| Coral Type | Required PAR Range |
| --- | --- |
| Softies | 50 to 150 PAR |
| LPS | 100 to 200 PAR |
| SPS | 200 to 400 PAR |

We recommend modern reef-spec fixtures like the AI Hydra 32HD or EcoTech Radion G6 to provide the spectrum corals actually need. These high-quality lights ensure your corals receive the right energy for photosynthesis. You can usually borrow a PAR meter from a local US reef club if you do not want to purchase one.

## Cause 3: Flow problems

### The Dangers of Incorrect Current

Our flow tests prove that while corals desperately need water movement, the wrong kind of current easily kills them. Too little flow allows detritus to accumulate on the coral surface, which keeps polyps closed and starts tissue necrosis. Too much direct flow acts like a laminar jet, causing severe tissue stripping on fleshy LPS and softies.

We also frequently find dead spots in areas of the tank with no flow, which accumulate waste and grow problem algae. Signs of incorrect flow include coral tissue receding exclusively on the flow-facing side. You might also notice polyps not extending or excessive waste accumulating around the coral base.

### Creating Random Sweeping Flow

Our preferred fix is to create a random sweeping flow using reliable pumps:

-   EcoTech Marine VorTech MP40
-   AI Nero 5 Submersible Pump
-   Maxspect Gyre Series
-   Jebao SOW Wavemakers

Popular options in the US market provide excellent random flow patterns. The VorTech MP40, for example, pushes over 4,500 gallons per hour while keeping electrical components safely outside the glass.

We suggest using multiple smaller powerheads distributed around the display over a single large one. This setup prevents harsh unidirectional currents and mimics natural ocean turbulence. Periodic rearrangement of your rockwork or pump angles will help eliminate stubborn dead spots.

## Cause 4: Pests

### Common Reef Pests

Our quarantine specialists find that pests are often the hidden cause when parameters check out and lighting and flow look right.

-   Aiptasia anemones
-   Acropora-eating flatworms (AEFW)
-   Montipora-eating nudibranchs
-   Vermetid snails

Aiptasia anemones are a major threat because they overrun the tank and severely sting neighboring corals. Flatworms literally eat coral tissue, with Acropora-eating flatworms being especially destructive to SPS dominant tanks.

We constantly battle red bugs, which eat Acropora and appear as tiny, bright red specks on the branches. Montipora-eating nudibranchs are another common US pest that specifically targets and eats Montipora bases. Vermetid snails cast sticky mucus nets into the water column, which damage SPS over time and irritate polyps.

### Identifying and Treating Damage

Our livestock inspectors also warn against certain nipping fish. Some angels, butterflies, and hawkfish develop a taste for expensive corals and eat them down to the skeleton. Signs of pest damage include tissue loss in specific patterns, such as bald spots always at the base of Montipora from nudibranchs.

> We often see the tips of Acropora dying back as a classic indicator of flatworm infestations. You might even spot visible pests crawling directly on the coral or surrounding rocks during nighttime viewing.

![Aiptasia anemones overrunning rockwork](/images/misc/aiptasia-anemones-covering-rockwork-next-to-stress.webp)

The solution is to dip the affected corals using proven commercial solutions like CoralRx or Two Little Fishies Revive. Our treatment protocols are covered extensively in this guide to 

coral dipping and quarantine

[/guide/coral-dipping-and-quarantine/ →](/guide/coral-dipping-and-quarantine/)

. You must address the source of the infestation to prevent a recurrence. Sometimes removing a problem fish from the display is the only permanent fix.

## Diagnostic order for why my corals are dying

### Step-by-Step Troubleshooting

We follow a strict diagnostic order when a coral starts dying to avoid guessing:

1.  Test core parameters
2.  Inspect closely for pests
3.  Observe water flow
4.  Measure lighting PAR
5.  Evaluate recent tankmate additions

Testing parameters like salinity, alkalinity, calcium, magnesium, nitrate, and phosphate is the mandatory first step. If any of those core numbers are way off, that is highly likely the cause of your problem.

Our second step is to inspect the coral closely under good light with a magnifying loupe. Looking for visible pests often reveals tiny threats like red bugs that naked eyes miss. Checking flow by watching how particles move around the coral base is the third diagnostic requirement.

### Finding Hidden Parameter Swings

We then check your lighting setup by taking fresh PAR readings and verifying the spectrum settings. The final check involves evaluating tankmates to see if a new fish has been added recently. The single most common diagnostic miss is assuming parameters look fine today, even though they actually swung a few days ago when you were not testing.

Our best advice is to test daily for a solid week to catch hidden chemical swings. This persistent tracking exposes the dangerous fluctuations that occasional testing completely misses. Keeping a detailed logbook makes identifying these subtle trends much easier.

## When to bring a sample in

We invite you to bring a clean, one-cup water sample to 

the store

[/contact/ →](/contact/)

 so our staff can run a full panel. The test covers salinity, calcium, alkalinity, magnesium, phosphate, and nitrate using professional-grade US testing equipment. If you have a problem coral, photograph it on your phone before heading over.

Our experts frequently notice that a quick smartphone photo reveals a pest you did not see in person. The diagnosis usually narrows down within a few minutes once the parameter data is sitting in front of the team. The final fix is simply a matter of stabilizing dosing, adjusting lighting or flow, and removing the identified pests.

We see incredible recovery rates when a struggling coral is caught early and treated properly. A coral that has been receding for weeks may not pull through, so fast action is critical. If you find yourself wondering why my corals are dying, get your water tested today, protect your investment, and bring your reef back to life.

## Frequently Asked Questions

Is coral bleaching reversible?

Sometimes. If you fix the cause quickly, zooxanthellae can recolonise. Persistent bleaching that lasts more than a few weeks usually means tissue loss is coming.

Why are my SPS turning brown?

Usually too much nutrient and too little light. Brown corals are alive but the zooxanthellae are using nitrogen heavily. Bring a water sample for free testing and we can pinpoint it.

Could it be my new fish?

Some angels and butterflies nip corals. Check your fish list against reef-safety guides. Removing a single problem fish often fixes mysterious coral damage.

![](/images/misc/wide-shot-of-specialty-aquarium-store-interior-wit.webp)

## Got a tank question? Come ask in person.

Free water testing, honest stocking advice, and a dedicated coral room. Walk in Monday-Saturday 10-6, Sunday 12-5.

Visit the Store

[/contact/ →](/contact/)

 

Call (941) 555-0178

[tel:+19415550178 →](tel:+19415550178)