Article By Peter Newman
Edited and added to by Think Fish

Stability of environment
The vast volumes of water in the sea mean that there is very little variation in the chemical parameters of seawater. Salt levels (salinity) and pollutants such as nitrates etc remain fairly constant. However having said that, experienced divers will tell you that there are constant currents coming from deep water, with variations in temperature and salinity flowing across the oceans. These tend to be temporary fluctuations and fish can adjust to these with relative ease. In the aquarium marine fish must be kept with this stability in mind, which requires a better quality of source water, additional filtration
equipment, and a more steady approach than freshwater fish.

The cycle of waste
The biological or nitrogen cycle is the same in salt water as in tropical or fresh water. Fish produce waste, which is highly toxic and combined with waste from dead fish plants, and food, is released as Ammonia. Bacteria in the filter system and in the aquarium break down Ammonia to nitrite, (less toxic), and then to Nitrate (less toxic again). In a tropical system the plants absorb Nitrate as food. In a Marine system water changes are essential to maintain this level at zero. Nitrates can also be removed in marine aquariums by using specialised filter media or in some setups, living rock, which contains living creatures, bacteria, and algae which process nitrates

Quality of Water
Tap water is intended for drinking washing etc. It is not of a quality suitable for marine fish. The Nitrates/ Phosphates etc are normally higher than the level expected in a Marine system, and a high content of heavy metals and other tap water pollutants will adversely affect marine fish and cause algae blooms in a marine aquarium. This is why the need for Reverse Osmosis (RO) water, which is essentially pure water, is common in marine aquariums. The disadvantage is that R.O. waters natural ability to maintain a stable PH value is reduced. In marine systems a pH between 8.1-8.3 is required and the water will need constant checking and buffering to maintain this value. Many fish losses result from PH crash where the level will drop to as low as 7.5 overnight due to a lack of buffering. Most retailers will stock buffers and mineral supplements which can be added to R.O. water, along with salt.

Filtration
Salt water requires high levels of oxygen. In the sea the waves and the sea crashing on rocks etc produce this. External filters have a limited capacity to hold oxygen since bacteria often deplete the oxygen before it reaches 50% of the media. Sponges create a build up of nutrients and pollutants, which encourage Phosphates and Nitrates. External filters may also have a limited capability to expand and once the maximum level is achieved, the filter cannot cope with any additional stock. Whilst external filters can be used in some marine aquariums adequately, it is worth looking at other options

Trickle Filters
Water from the aquarium trickles through a filter media (Such as Bio balls) and remains rich in oxygen because the media is exposed to the air. The area available for bacteria to grow is large, and unlike an external filter can expand to cope with the stocking levels of the aquarium. These types of filter are excellent in breaking down Ammonia, but do not remove Nitrates. Therefore regular water changes are essential.

Deep Bed Sand Filters
In these systems a sump is installed in the cabinet or other suitable area. There are three main chambers. The first contains 'Bio balls', or other media, which can be either exposed to open air (trickle filter) or submerged in the water. This breaks down waste to Nitrite and Nitrate. The second chamber contains 'live' sand and Caulerpa (Marine plant-like algae) this absorbs the Nitrate as food. The sump is lit with bright lighting such as a 12K light tube 24/7 to ensure maximum growth.
The final chamber contains return pump and Protein Skimmer. The heater can also be housed in the sump reducing the need for equipment in the tank.

Ideal Water parameters for a marine system are:
Salinity 1-023/1.024
PH 8-3
Temperature 78
Ammonia Zero
Nitrite Zero
Nitrate Zero




Taking your time is important
Each time a fish/coral is added to the aquarium the pollution levels may rise, because bacteria will only develop to meet the needs of the existing stock. New additions therefore produce waste over and above the capability of the filter and the bacteria will need to adjust to take the extra load. More than one fish, or small introductions can result in disaster. Fish /corals can only be added when the waters readings are within ideal parameters.

Sounds hard?
Many people give up on Marines saying they are too hard to keep. We import fish weekly from Indonesia, Singapore, and other parts of the world. They travel in plastic bags with limited water and most survive for 18 hours or so. Long-term pollution is what kills fish, along with impatience to buy fish. I have kept many marine fish including Damsels, Yellow tangs, and Angels for in excess of 15 years. It is more demanding than tropical and the initial investment higher. Cheap isn't a solution. Despite this, with proper care, marine fish are long-lived and well suited to aquarium life; they are not hard to keep if they are kept correctly.

Invest and reward
Invest in the largest tank you have the space for and can afford; the larger the volume, the easier to manage. It takes up to twelve months for an aquarium to mature to a level of keeping difficult fish and hard corals. During this period standard 12k T8 tubes or T5 tubes are adequate. Some aquatic shops will sell you aquariums and equipment, which may not be suitable for Marines because they don't have the specialist equipment needed to maintain a healthy environment. Check on what you're buying and apply the above information.
Finally. We try to reproduce a bit of the reef in our homes. Water flow is essential to provide particles of food for corals, as is the movement of surface water since gasses exchange at the surface. Ensure that corals actually move in the aquarium with water flow, if they don't they can't feed