A comprehensive article covering 20 of the most

This piece of equipment is connected to your top-up unit that tops up with RO water. As you can see

Knowledge. (Do your homework)

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.
6. 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.
7. 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.
8. 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.
9. 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.

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.

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.

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.