Before we start discussing Coral health and related diseases we must distinguish between the three types of corals one gets:
Soft Corals
These are the corals that have no visible skeletal structure, e.g. Pincushion, Colt corals, Kenya tree etc.
LPS Corals
These are your large polyp stony corals, e.g. Frogspawn, Trumpets, Brain corals etc.
SPS Corals
These are the small polyp stony corals e.g. Acropora, montipora etc.
Requirements of healthy corals.
Let’s discuss what healthy corals should look like before we discuss diseases. A healthy coral should be open with good polyp extension, vibrant colors and should show a good growth rate. A coral that is stressed will not show polyp extension or good growth rates and these are symptoms to start showing concern.
Effects of our water on corals.
There are a few parameters that have to be watched when keeping corals, the most important of these being temperature as corals are happy in a very narrow range and temp can effect on other parameters.
1. Temperature. This is very important as the coral reefs around the world generally occur in the tropical climates; the biggest difference between these reefs and our systems is the amount of water available. The higher the temps climb in our little systems the less the oxygen content of the water. A good temp to strive for is between 26/27 deg cel. The most important factor here is stability try not have large swings in temp as this causes stress to the coral.
2. Your highest critical temp for corals is about the 30degrees at this temp your corals will start to droop and look like melted ice creams. Fish will begin breathing rapidly at these temps. It is far easier and cheaper to heat the water than it is to chill it. If you do keep a reef tank with the correct lighting, chances are in summer you will have to chill the water.
3. Salinity. Also a very important parameter not the actual reading itself as much as stability once again. Reef tanks can be kept between 1.022 and 1.026. If your salinity is too high or too low again stress will be caused to the corals. The most accurate way of reading the salinity is with a refractometer. When the salt water evaporates you must replenish with pure fresh water as the salt stays in solution and if top ups are done using salt water your salinity will climb way too high in a very short period of time. Reverse osmosis or distilled water is perfect for this.
4. Lighting and water movement. If you over light a coral this will cause the coral to bleach and turn white it will generally starve to death after this. When placing a coral in the aquarium for the first time place near the bottom and gradually move up over the next few weeks. Water flow is different for the different types of corals. The one thing to remember with water flow, it is more important than light as your corals respiration depends on this flow. This assumption is made on the fact that your corals can survive with out light for 3 or 4 days but during a power failure when your water flow stops it is only a matter of hours and your corals will be in serious trouble. Food, nutrients and fresh oxygen rich water is brought to the coral and the waste product is carried away with water flow. The coral will basically suffocate in its own waste if the flow is too low.
5. Phosphates. The biggest addition of phosphates to a system is us the aquarist in the form of food that we feed our fish, this is considering you are using pure water for evaporation top ups and it is phosphate free. Now if you have a heavy bioload of fish and you are feeding regularly please make sure your filtration is geared for this especially the protein skimmer. Phosphates should be kept at 0.02 ppm; phosphates are actually important to a system as corals do absorb it and use it as a food source but only in minute quantities, some of the research being done at the moment shows a system with phosphate at 0 causes stress in corals and slowed growth rates.
Large quantities of phosphate also have a negative effect on corals and your system as a whole. Elevated levels will cause algae growth as it is one of the main food sources for plants, SPS corals will turn brown, instead of showing their vibrant colors. Should the levels continue to climb your corals will go into stress and eventually die? Control of phosphates is fairly easy good skimming and or phosphate remover.
6. Nitrate [NO3]. This is the result of the end product of a partial nitrogen cycle and is fairly non toxic to corals and fish. Elevated levels here will generally cause algae blooms and if phosphate is present at the same time you could experience algae blooms of biblical proportions this is termed high nutrients in your system. Nitrate should be kept below 5ppm but can be tolerated up to 10ppm. Aquarists use all sorts of methods to control nitrate the most popular is natural filtration, the use of live rock, a deep sand bed and a refugium with one or other macro algae’s are very popular. Other methods are Plenums and Nitrate filters. All of the above are very effective in the control of nitrate.
7. PH. Ph should be around the 8.2 mark; it will dip in the evening after lights out and rise again the next day. This ph swing should be kept to a minimum so as not to cause stress to live stock, a swing of 0.2 is tolerable so if the ph at light out is 8.2 then it should not dip below 8.0 at its lowest point. Ph is affected by many things your Carbonated hardness [Kh] being one of them. KH should be maintained between 7 and 9 Dkh. Systems running Calcium reactors will generally run at a lower Ph because of the presence of CO2 but make up for it in the stability they ensure.
8. Calcium and Magnesium. These are two very important minerals in sea water and should be maintained especially when keeping LPS and SPS corals as their health and growth depend on it. Calcium can be supplemented in many ways, 2 part additives, and Kalkwasser or calcium reactors. Calcium and Kh should always be added in equal portions as stated on the bottles in 2 part additives as adding one with out the other can cause an ionic imbalance. This is why calcium reactors are as popular as they add equal quantities of both. Calcium should be maintained between 360 and 425. Magnesium between 1200 and 1300ppm.
Recognizing , preventing and treating diseases.
The five major problems of coral loss.
Physical damage.
Placing of coral in a firm position is a very under estimated problem. Corals that constantly fall off rocks, or continuously handled will normally lead to some sort of parasitic or bacterial disease or some sort of bruising.
Sediment damage.
The damage caused from sediment in one’s fish tank can cause a great deal of problems. If one does not have enough circulation with in the fish tank.
It is also recommended to stir the gravel in one’s fish tank at least once a month, this helps to prevent massive sediment buildup. When one stirs the gravel or has to move a rock. the sediment buildup is very visible. This can be a real problem due to sediment settling on corals that aren’t able to deal with it. This in turn will start a bacterial problem with certain corals and cause degeneration and eventual probable death. Corals that are able to exuded a lot of mucus will normally be able to clear themselves of any sediment.
Damage caused by fish.
This must be one of the biggest problems in a fish tank. The balance between the correct type of fish as well as the number of fish selected for the size of tank one has. Any of your bigger wrasse as well as angels are generally a problem.
Algal destruction.
Algal destruction is any other real problem in one’s fish tank, may it be various forms of algae that eventually take over the fish tank, or algal cells with in the coral eventually die due to various problems such as poor lighting or water quality. In some form or another.
Diseases.
The diseases that affect the corals are divided into two categories; they either affect the polyps or the zooxanthellae in the coral.
Generally coral diseases can be broken up into the following categories:
Stress.
Generally stress is caused when a coral is not happy in its environment and this should be rectified ASAP, when a coral is under stress it is in a weakened state and is susceptible to all sorts of diseases. One of the symptoms can be caused by over lighting or under lighting. Corals placed to close to one another [causes stinging and burning one another]. Water flow can also play a part being too much or too little, as well as stability in temperature. The other factor that causes stress is our general water conditions.
A consciences aquarist will know what these parameters are and will test the system regularly. Another form of stress to a coral is when a fish keeps nipping at it, as it has no form of defense against this. Please research all live stock you want to keep, may it be a coral or fish. This will all go a long way in preventing disease.
Parasites.
There are many parasites that attack corals. We will discuss the few that are commonly found.
1. Flat Worms, generally will attack all corals and are very difficult to identify as they sit on the under side of corals out of the light to stay out of sight of predators. They are small and look like a miniature grain of rice. Your coral generally shows signs of stress when infected, try to check your corals at night with a torch as this is when most parasites can be detected. Cures are numerous from medicines like Pro Coral Cure, adding predators or fresh water dipping if the coral can be dipped. Predators for these parasites include the Mandarin and the Scooter blenny.
2. Snails, there are many good snails that are added to a marine system basically for algae control but there are many snails that live off the flesh of the corals. Your coral will again show signs of stress and show the snail trail where it has crawled. Again these critters can be spotted at night with a torch and can be manually removed. Predators of snails are your wrasse family especially the six line, banana wrasse and the 8 line wrasse. If you find any snail that you did not add to your system rather remove it as they can lay thousands of eggs all of which will hatch in our systems and soon you could end up with an epidemic of snails.
3. Crabs. These critters come in all sizes and are very difficult to detect but again your best chance is at night after lights out. The general rule of thumb is if it’s hairy get it out. They will attack all corals. The crabs that attack SPS corals are very small and resemble the crabs that host in so many of the Acropora colonies. They are very difficult to remove as they hide in the branches of the colony and have to be manually removed as even the predators cannot get them out.
4. Bristle worm, although not a true parasite of corals it does deserve a mention here. There are many worms that fall into this category and only a few will prey on corals and some on fish. Fortunately for us the most common ones found in our systems are scavengers and very effective scavengers at that. The problem often arises when they reach epidemic proportions. This normally occurs when the system is being over fed and there is plenty waste food lying around. The myth that they attack corals is just that, a myth. When a coral is being attacked it is usually a coral that is already dying and has some rotting flesh on it. This rotting flesh is a magnet to any scavenger, worms, shrimps, hermit crabs etc. So the cure for bristle worm is do not overfeed the system and keep your corals healthy. A general word of warning here never remove a bristle worm with your bare hands, there is a reason they are also known as fire worms.
An observant aquarist will always know when his corals are under attack from parasites/predators as you will notice the coral is stressed and not opening, pieces will be missing where these critters have been feeding and a plan of action must be taken in order to save the coral. Predators can be added to keep the population of the parasites to a minimum.
Bacterial diseases
The first thing to note about bacterial diseases is that they are extremely contagious and can spread through an entire colony in a matter of hours. You must also take extreme care when removing a coral that is infected as the bacteria strands come loose and can land on other colonies and start the infection all over again. The best method is to siphon the infected area with a piece of airline tubing and make sure the area is clean before removing the infected piece. Bacterial infections will generally start when a coral is stressed due to the reasons discussed above.
1. Soft corals will show a patch of dark brown to black on the body of the coral and there will be no polyp extension in that area. Treatment is to siphon the area clear, and keep a close eye on it. If the infection returns the coral should be removed and if possible that area cut out using a sharp blade or pair of scissors. The main reason for the removal of the coral besides being easier to work on is. The coral will release a quantity of slime when you cut it, and other corals may even be re-infected. If in doubt rather discard the coral.
2. LPS corals. These corals generally show a jelly like substance around the entire head or section. The jelly can be a white or brown substance and in a species like trumpet or frogspawn where the coral has multiple heads this can spread very rapidly and wipe out a colony over night. Again the cause is often stress induced. To treat the coral siphon out the infected areas and remove the coral from the water column. You will notice the infected area has a pungent smell. Remove the infected heads of the coral using a pair of side cutters. If it is one of the species that has numerous heads and make sure the heads around are not infected, try leave the coral in isolation for at least 48hrs to make sure the infection has not spread. In the corals such as the Brains and Donuts you can try cutting the infected area away but often this stresses the coral even more as you try hack your way through with a hacksaw. The better bet with these types may be a dip in pro coral cure or a fresh water dip for about 5min.
SPS Corals
There are 2 main diseases that SPS suffer from and those are RTN and STN and each will be discussed individually.
1. STN. This stands for slow tissue necrosis, and is more often than not related to water quality which leads to stress in the coral. The coral starts to loose its flesh from the tips and starts to turn white from the tips back towards the base. Treatment is to immediately check water parameters if it continues the only solution would be to cut off some uninfected areas and start the colony again.
2. RTN. This stands for Rapid tissue necrosis and is almost same as above but generally starts off at the base and works its way to the tips but happens very rapidly and you could loose the entire colony in a matter of a few hours and may also be bacterial related. The only solution here is to cut off some of the uninfected pieces and restart the colony.
In both the above cases the reason should be investigated and an answer found, so the problem can be rectified. Other wise an entire display could be lost in a matter of days. Please note SPS pieces are very sensitive to stings from other corals so when placed in the aquarium should be placed at a safe distance so as not to touch another coral.
Conclusion.
In all the above scenarios it is up to us the aquarist to observe the health of the coral and this is why observing the tank is so important. Take the time every day to observe each coral individually.
