Learn How To Identify And Solve The Four Most Common Coral Health Issues

Most of us will eventually go through a phase with our reef tanks where the corals just don’t look so great. Different corals show stress in different ways and this could be refusing to open, loss of tissue both slowly and rapidly and worst case scenario bleaching or abrupt death.

Our goal in this episode is to show you how to be prepared, what to look out for and how to get past some of the most common coral issues. We are specifically focusing on the easier to keep soft corals and LPS we chose for our 40 gallon tanks and grouped the ailments by four distinct causes.

Side by Side Duncan Coral

Water Parameters

The number one cause of problems with your coral will be issues with your water parameters, it is particularly obvious when a variety of different corals are showing signs of stress at the same time.

Consider the following four parameters the most critical, evaluate them first and in this order.

Salinity being number one because when salinity is off, everything is off. Your target is 35 ppt. One point in either direction probably won’t cause anything major but beyond that, the risks become increasingly higher the further away you get. In either case, you want to correct it immediately.

Refractometer Scale

Reducing salinity is as simple as removing some saltwater and replacing it with the same amount of RO/DI water. Increasing salinity is just adding saltwater to your tank by letting water evaporate without any freshwater top off to the tank, then fill it back up with saltwater. For larger swings say 5 points or more, a series of large water changes will be most effective.

Hanna Instruments

Alkalinity is the most important single parameter and if you are going to take away one bit of advice, this is it. If you maintain stable alkalinity levels you are 100 times more likely to be successful than if you do not. Right after that in order of importance is calcium and, to a lesser degree but still important, magnesium.

If you find any of these parameters to be off, the low cost method of correcting them is our popular BRS Reef Calculator and the appropriate BRS Pharma solution. To learn more, simply check out the 5 Minute Saltwater Aquarium Guide Episode #19 - Calcium and Alkalinity.

Bright fish tank


If you run into issues right when you add an otherwise healthy coral and everything else looks good in the tank, there is a high likelihood it is because the lighting or PAR is too high for the coral. Too much light is toxic to the coral and can kill it in a matter of days. Where as not enough light may take many weeks to show signs of distress and then months to die.

Corals like the ones we added in these tanks will often show signs of not enough light by stretching out and reaching for the light as well as gradually turning brown.

Bleached coral

Corals receiving too much light will shrink up, retract polypes, bleach white or close and sometimes start to loose tissue. If this happens to a new coral, move it further away from the light source (bottom or sides of the tank) and give it plenty of time to recover, 2-3 months or more.

If this happens when you add your first batch of corals or after you make adjustments to your light’s output, then turn the lights back down. Just remember the color and intensity sliders are not a toy, this is life support for an organism that depends on you and they thrive on stability.

Coral frag

Corals will adapt to most lighting conditions within reason of what is ideal so long as you leave them alone and let them acclimate. Even the slightest change in lighting is an immediate set back in this case.

Par Meter Rental

When dialing in your light for the first time, rent a par meter to gauge how much light your corals are getting. For $60, it is well worth the confirmation that your light spread and output is spot on. For soft corals and LPS, you are shooting for 50-150 PAR throughout as much of the tank as possible.

Water Quality

This could be either slow deterioration of water quality from less than stellar feeding or maintenance practices or from an unintentional contaminant. To identify this, start by looking at nitrate and phosphate levels. If they are sky high, they may actually cause stress but more so just a general indication of poor quality, polluted water.

Most hobbyists shoot for nitrates levels less than 5 PPM and phosphate levels of 0.1 - 0.2 PPM. In established tanks where algae is less of a threat, nitrate can often be found at 10+ PPM and phosphate levels as high as 1-2 PPM without issue. If you are going beyond these levels, consider changing your approach to maintenance and feeding altogether.

Bucket Test

The bucket test is also another easy way to see exactly how clean your water is. Pull out a bucket of water from your tank and compare it with freshly mixed saltwater. You will see right away if your tank water looks polluted based on the color of the water. It doesn’t need to match perfectly but will give you a sort of pulse on your tanks water quality.

There is also the possibility of foreign or unintended pollutants like lotions, oils , soap or other residues from your hands. Aerosols and harsh cleaners of any kind used near the tank are a big no no and pretty much anything else that could accidently get into our tank.

ROX 0.8 Carbon

If you suspect a contaminant, your first approach would be adding or changing out your carbon. It is best to use a fluidized reactor or powered filter of some kind to employ the carbon for effectiveness sake. If you don’t see things turn around in 24 - 48 hours, move onto some water changes.

Contaminants can be serious so past the point of using some fresh carbon, don't fuss around with any specialty filter media and attempt to try to target something or avoid a water change.

Just do some large water changes every other day until the entire tank volume has been swapped out. Roughly 30% - 40% every 2 days and your tank should bounce back.

Large water change

In the event you have a serious contaminant and things are dying or deteriorating rapidly, hardy corals like the ones we chose can withstand even larger water changes in the realm of 50% - 90%. Be sure that water is mixed, heated and ideally match the pH of your tank. This is better than watching things just fall apart in front of your eyes.

In any case of which a large water change is required to “save the tank” you want to reevaluate your routines and maintenance practices as well as try and identify what got into the water that caused such a problem so you can avoid it in the future.

Stretching Goniopora coral

Pests, Fungus or Infection

These types of things often only affect one specific coral or type of coral in your tank. For example, Zoanthid Eating Nudibranchs only prey upon zoanthids and nothing else.

In these cases it is time to remove the coral and dip it. The exact type of pest or parasite will negotiate the exact dip. For most common pests and parasites, Two Little Fishies Coral Revive or Brightwell Aquatics Koral MD Pro are excellent choices.

Coral Dip

After dipping your coral, look closely to see if you can identify anything that fell off the coral during that dip. If you see something that concerns you, take a picture and share it on Reef2Reef or the #askBRStv Facebook Group for more information.

If you suspect a fungus or microbial infection there are two paths. An iodine based dip such as Brightwell Aquatics MediCoral or Tropic Marin’s PRO-CORAL CURE. These are great for Green Star Polyps or Zoanthids that simply won’t open or Euphyllia like Frogspawn, Torches and Hammers that are deteriorating.

With Euphyllia, consider cutting off the infected area to stop the spread of the infection.

Euphyllia coral tissue damage

One of these solutions or approaches should solve your issue for you in a vast majority of cases. If it doesn't, the best thing you can do is take detailed pictures and share them with the reefing community. Be as detailed as possible with high resolution pictures, description of what has happened and the exact type of coral.

What’s Next?

That is a great question and exactly what we plan to cover next. After the first 12 months of keeping your first reef tank, where do you go from here? In the final episode, Ryan shares ways you can continue to access the most trusted reef aquarium resources.

Most households have an unsolved Rubiks Cube but you can esily solve it learning a few algorithms.

5 Minute Saltwater Aquarium Guide Episode #29

Looking for a different topic or have questions? You can binge the entire 5 Minute Saltwater Aquarium Guide playlist right here on our website. We also invite you to join the #askBRStv Facebook Group which is a free resource for you to ask questions, get advice, interact with other hobbyists and get your daily reef aquarium fix.

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