Every problem with every reef aquarium is just a matter of too much or too little of something!
I am very regularly called out to solve problems with people’s reef aquarium because a coral is not doing well. I have discovered that there is only ever one of two things wrong with any coral. It either has too much of something or not enough of something. For example it is always problems like too much flow, too much phosphate, too much harassment from fish or not enough light, not enough trace elements, not enough space between it and the next coral. Every time I solve a problem it is always too much or not enough of something, it is that simple. The trick is to find out what it has too much or not enough of.
Light is a major consideration for all corals. It is important to try to replicate the lighting conditions that the coral would naturally experience. The major considerations here are intensity and colour. As the water gets deeper the intensity decreases and mainly only the blue in the spectrum is able to penetrate, so corals found in deeper water should be kept under high Kelvin globes like 20,000 kelvin and/or be placed lower down in the aquarium. Corals from shallow water prefer lower Kelvin globes like 10,000 kelvin and are best positioned at the top of the aquarium. Using this knowledge it is important to consider where you are going to position a particular coral in your aquarium before you purchase it.
The aim of your rock structure really should be to present as many positions possible for corals to be placed on allowing them maximum exposure to the light. Ensure that you position each coral to maximize how much light they can gather. Corals that don’t require any light should be positioned where there is little to no light as too much light may create an overgrowth of algae which the coral will find hard to compete with. These corals also require regular hand feeding and prefer more flow as they rely on it for food.
Corals have an amazing ability to adapt to different conditions but the more we understand the natural conditions of a particular coral the betters its chances are. One of the main ways that a coral will adapt is to expel its current zooxanthellae and replace it with new ones. This will often cause the coral to appear to change colour.
Water flow is also a major consideration for coral survival. The ocean current washes away the coral`s waste and the waxy film that it produces to free itself of algae and sediment. Some corals are naturally found in conditions with very powerful waterflow while others are found in very calm areas. This consideration will effect where it will do best in your home aquarium. If it looks like the coral is being battered around by the current and it is not opening properly, then you can bet it is positioned where there is too much flow. Try moving the coral to a position in the tank further away from the waterflow and see how it reacts.
Also watch to see if the tentacles of the coral looks stagnant and if sediment is forming on the coral. These are a sign that the coral needs to be in a position with more waterflow. The more you know about the coral, the easier it is to play this game, but at the end of the day it is really the coral that tells you what it wants.
Some corals of similar species can be placed right next to each other while different species need a considerable amount of space between each other if you want both to thrive. In nature many corals have to compete for space using toxins to suppress and sting each other. It is often easy to see if a coral is suffering due to competition because one side of the coral closest to the aggressor will be closed while the other side may still be thriving. When you see this, it is important to move one of the corals to allow them both to grow.
Most corals get most of their nutrients from the light, while others total rely on filter feeding from the water. Not enough organic food present in the water will starve some corals, while too much will affect others. Some corals come from nutrient-poor water and cannot deal with even low levels of nutrients in the water, while for others these nutrients are a must. If you are getting too much algae in your aquarium, especially if it is well fed, it is important to maintain low phosphate levels. Phosphate is the main reason for algae problems and this is associated with feeding. Adequate use of phosphate sponges will ensure this is never a problem. People rarely use enough phosphate reducing media in order for it to be effective against algae. So once again the same thing: too much of something or not enough of something.
Trace elements seem to have different effects on different corals. Various trace elements are crucial for the long-term success of some corals, while those same elements don’t seem to be as important for other corals. Consider that most trace elements don’t stay in solution for long so they have to be replaced regularly and also that many trace elements are toxic if they are overdosed. For that reason, it is essential to ensure that you do not have too high or too low levels of trace elements in your marine tank.
Some corals just need a little peace in order to thrive. It is important to regularly sit quietly a fair distance from the tank to allow you to view the behavior of the fish in your aquarium. The fish will often respond differently when they sense your presence in the room. Allowing your fish to exhibit their natural behaviour will often reveal that a particular coral is not opening and doing well because it is being harassed by a particular fish, commonly a Wrasse or an Angel. Even if a fish isn’t eating the coral, it still may end up killing it. A nip here and a nip there may stress the coral and cause it to close up regularly enough to effect it long-term. Not enough peace can be a problem even for corals.
Temperature is the most common problem in reef aquariums. Not enough heat is rarely a problem these days because of how reliable common aquarium heaters are. Too much heat is the big killer! Anyone that lives in areas with warm summers will place their reef aquariums at risk every year if they don’t have an aquarium chiller. Temperature over 27’C for extended periods of time can be enough to effect coral growth long term, 29’C can kill many types of corals within days.
Running a reef aquarium you must be concise with how much salt there is in your water. Corals seem to do best if the salt level is on the high side e.g. 1.025, while fish tend to introduce better at a lower salt level e.g. 1.020. Because of this I suggest running an established tank at 1.025 and a new tank or a tank likely to be accepting new fish at 1.020. I commonly recommend people lower the salt in their established tank when they are adding new fish. This will reduce the osmotic pressure on the new fish and allow it to be introduced with a lower chance of suffering from stress and/or parasitic disease such as white spot. Often I find reef aquariums full of thriving fish with struggling corals- this is because the salt level is run too low. So the big question is too much salt or not enough salt.
Once you place a coral in your aquarium, watch it for 3 weeks and if it is not reacting the way that you know it should then move it to another position, keeping in mind whether it may be getting too much or too little light, flow or space. It is that simple- too much or too little.
The aim of every reef-keeper really should be to have an aquarium that is truly thriving, not just surviving. If your corals are not growing then they are dying. Consider that if your corals grow they will outlive you, and if they only live for a year or so then that is how long they take to die. If they are dying, then they have too much of something or not enough of something - it’s that simple.
Good luck and enjoy, Paul Talbot