Acropora corals are known to be ‘hard to keep’ and many beginners (See: Beginners Guide to Keeping Corals)steer clear for this reason, however, if you do your research and have a little patience you too can have a successful SPS tank. Acropora belong to a group of corals referred to as Small Polyp Stony (SPS) corals which, as a group, are thought to be harder to keep than other corals. It should be noted that the term SPS is not a scientific classification, rather it is a term invented by hobbyists to distinguish between large groups of corals. The following is a guide to keeping and growing SPS corals, with a particular focus on Acropora.
Balance is Key
There is no silver bullet to keeping SPS corals healthy and colourful, however, appropriate balance and stability will greatly increase your chances of success when these types of corals. Temperature stability is critical as large variation in temperature wreaks havoc on SPS colonies. Using a controller will ensure that temperature remains constant. Controllers can switch the heater off in case of malfunction and switch fans on if necessary. Fans and water coolers help prevent the temperature from rising above acceptable levels. This is helpful as the intense lighting required to promote rich colours in SPS can generate a lot of heat.
It is hard to overdo lighting when keeping an SPS dominated tank. However, it is still important to properly acclimated all corals to your tanks specific light source. When deciding on lights the more powerful, the better. However, it is important to remember that on natural coral reefs, corals only receive about 6.5 hours of intense sunlight per day. Therefore, if you intend to keep your lights on for longer than 6.5 hours make sure the lights are gradually increasing in intensity until they reach a peak and then gradually reducing in intensity. The lights should be at peak intensity for approximately 3-4 hours. If you are using LED lights, then this gradual increase in intensity is easy as most brands allow you to set this kind of light schedule. However, if you employ multiple T5 lights or metal halides, you can switch the bulbs on independently over the course of a few hours.
Flow is vitally important in an SPS tank. There are several reasons for this. Flow helps keep detritus from collecting on the bottom of the tank, which helps keep nitrates and phosphates from accumulating. Strong circulation also helps to deliver food and nutrients to corals and helps to prevent problematic algae from taking hold in a tank. Finally, good circulation creates surface agitation, which increases oxygen levels and replicates the light refraction seen in our natural reefs. Flow should be approximately 50 times the tank volume. The flow should be varied to prevent tissue loss which results from laminar flow patterns (parallel flow patterns).
It has been noted that high sedimentation levels have killed wild SPS colonies. Many hobbyists choose to keep bare bottom aquariums for this reason. The bare bottom helps to prevent the accumulation of sediment and gives you more flexibility with flow as the high flow required in an SPS tank will often stir up the sand bed resulting in a sediment filled water column. The use of a bio-pellet or zeovit reactor replaces the need for a refugium or sand-bed, and allows the aquarist to remove any unwanted debris easily.
Calcium and Alkalinity
When keeping an SPS dominated tank it is critical that you maintain calcium and alkalinity levels as these nutrients are rapidly absorbed by SPS corals. There are numerous ways of maintaining calcium and alkalinity levels, all of which work. Choose the method that works for you and will allow you to achieve the most stable parameters. You should test alkalinity at least twice a week and calcium at least every other week. Alkalinity affects a wider range of water parameters than calcium does so should be tested more frequently.
Nitrate and Phosphate
To prevent browning, there must be an almost complete absence of nitrate and phosphate. Although small, slightly detectable levels of either are permissible and will still allow you to have beautiful SPS corals, levels should be kept as low as possible. As a guide nitrate levels should be kept between 1-10 ppm and phosphates between 0.02 and 0.1 ppm. It is important to understand that the colours we see in corals are not the result of the symbiotic algae that live inside the corals and provide them with food. Instead the colours are the result of a layer of skin that protects the colony from the harsh rays of the sun. In the marine aquarium we have to balance nutrients levels so that there are enough nutrients for the symbiotic algae to grow, so that the coral gets enough food, but not enough to cause the corals to turn brown.
Keeping SPS and LPS corals together
Because of the different preferences in light, flow, feeding requirements and aggression levels, LPS and SPS corals shouldn’t be kept together. LPS typically require more frequent feeding with larger foods, with higher levels of blue light and laminar (parallel flow patterns) flow patterns that simulate the reef at depth. SPS usually need smaller foods, with whiter light and with strong, chaotic flow patterns that simulate the shallow reef.
Acropora is one species that comes with its fair share of pests. While many aquarists don’t extend quarantine to corals, in the case of acropora it becomes very important. A coral quarantine tank doesn’t have to be complicated. It can be as simple as a bare tank with egg-crate at the bottom, heating and filtration equipment. All new corals should also be dipped to ensure that incoming pathogens and parasites are eliminated. To ensure that new corals are healthy before transferring them into the display tank you should quarantine for at least 2 weeks to one month.