Marine – Set Up & Maintenance

Marine – Set Up & Maintenance

Guidelines for setting up a Marine Tank


Marine fish are some of the most beautiful fish available, and their interesting behaviour, bright colours, and wide range of body shapes and sizes lend interest and colour to the home aquarium.


Their care requirements are different to those of freshwater fish however, and their tolerance for variations in such parameters as temperature and pH is less than that of freshwater fish. Parameters that are tested are Nitrites, Nitrates, Phosphates, Ammonia, Calcium, Alkalinity, Magnesium and Salinity – which is balanced at 1.025. The ocean itself is remarkably stable, with very little fluctuation on a daily or even annual basis, and for that reason it is very important to maintain a stable environment for any Marine fish held in an aquarium. It is important to spend time in establishing the tank well before adding any fish, and to monitor the conditions in the tank regularly once it is established. Many people achieve this, with the establishment of a regular routine and a few good maintenance habits.


Checklist for setting up your Marine Tank


  • Tank:

The tank should be as large as possible for the space you have provided. The larger the tank, the more stable the water conditions (which as previously mentioned is extremely important). Also ensure the tank is the appropriate size for the fish you will be housing (eg. Active, mobile swimmers such as Tangs require a larger tank than clownfish.)


  • Filtration:
  • Under gravel filters are generally not recommended, as they are easily clogged by sand. Due to their size, they are also usually not effective enough to cope with the large amount of water required in marine systems.
  • Hang on back filters provide gentle water movement and provide good bio-filtration but not much mechanical filtration. They will suit a small tank with 1-2 small clownfish.
  • Canister filters provide excellent mechanical and biological filtration and can be used for chemical filtration. They are usually used in conjunction with other filter components.
  • Protein skimmers are excellent at removing nitrogenous and organic compounds before they need to be broken down by the biological filter. This is essential for Reef Systems.
  • Live Rock in conjunction with good water movement provided by powerheads creates excellent nitrification and denitrification because of the large surface area of the rock.


  • Temperature:

The ideal range is 24-27°C and is controlled by heaters and/or chillers which are either installed within the tank or run separately from the sump.


  • Substrate:

It is best to use a calcareous substrate such as crushed coral or aragonite. These substances will help buffer the pH. The size of the substrate should not be so small as to get sucked into any filtration, but not large enough to pose problems to sand sifting fish such as gobies. The average size used is around 1-3mm.


  • Decorations:

Should be made up of substances that will not negatively alter the water chemistry. Dead coral, lava rock and coral rubble are all suitable choices. Live rock will also perform biological filtration. Only cured live rock should be added to an established tank, as premium live rock will have flora and fauna that are still dying off and which will create ammonia spikes. Premium live rock may also introduce unwanted animals into your established tank.


  • Test Kits:

Good quality test kits are essential to test for the above-mentioned parameters. Electronic meters are available, but expensive. To measure the specific gravity of the water, you need a hydrometer or refractometer. There are 2 types of hydrometers: the glass type that floats (and usually measure temperature as well) and the plastic kind with a floating arm. Refractometers are more accurate than hydrometers.

  • Water:

Marine tanks require the addition of salt, to mimic the condition of sea water. Use good quality marine salt that contains no nitrates or phosphates and has all the trace elements needed for marine organisms. Rock salt or conditioning salts cannot ever be used as a substitute. Natural sea water can be used, if it is obtained from an unpolluted source. A good source of water is RO water, or Reverse Osmosis Water. This is water that has been treated by having its contaminants removed naturally.


  • Lighting:

For a fish only tank, lighting is not crucial. Reef setups require specific lighting, such as metal halide, high output T5, actinic lighting and/or LED lighting.


Establishing your Marine Tank

  • Initial Set Up:
  • Day 1: Decide on the location of your tank before you start. Ensure that it is out of draughts and direct sunlight. Fill the tank with water to the desired level.
  • Set up power heads, filters and heaters. Turn them on and leave overnight to mix. DO NOT TURN ON YOUR ELECTRICAL EQUIPMENT UNTIL THERE IS WATER IN THE TANK AND YOUR HANDS ARE COMPLETELY REMOVED.
  • Test temperature and raise/lower the thermostat if required. Test the specific gravity and add fresh water if the reading is too high or marine salt if the reading is too low.
  • Add substrate and live rock and let cure for a few weeks (add small amounts of food and rock/sand from established systems to seed biological filter). You can add Mollies, which have a high tolerance to salinity to ‘seed’ the filter.
  • Test ammonia and nitrite regularly to determine when appropriate to start stocking with fish (slowly). The nitrogen cycle in marine systems is much slower than of freshwater systems. It may take up to 6 weeks before the cycle is complete, and nitrates are produced.


  • Introducing Marine Fish to your tank:
  • Before starting, test the tank water once again. Ensure all water parameters are correct.
  • Before purchasing fish, ensure that all requirements (feeding, hiding spots, room to grow to adult size) of the species can be catered for and ensure that the fish you have chosen will be compatible.
  • Once you have purchased your fish, immediately take them to your to your home. Do not leave them in the car and do not place them in hot areas.
  • Float the bag in the aquarium to acclimate the temperature. Do not open the bag at this point. Leave for 15-30 minutes.
  • When ready, use a clean, sterilised net to catch the fish from the acclimatisation container and put into the main tank. In some cases, fish can be placed in a floating basket within the tank, while it becomes familiar with its new home and new companions. This also helps the existing fish acclimatise to the arrival of a new tank mate. Using this technique also helps you identify any aggression, without the fish having the opportunity to fight.
  • Ensure that the lights are off and that there are plenty of places to hide for the new fish that nay come under scrutiny from existing tank mates.
  • It is not unusual for fish to hide for several days until they become accustomed to their new home.
  • Do not feed on Day 1. Don’t be concerned if the fish do not feed for the first 3-4 days.


Suitable Fish


  • Hardy fish which are suited to beginners include Damsels, Clownfish, Blennies & Gobies, as well as some Tangs and Wrasse.


Stocking Densities


  • Fish Only Tank:

Stocking densities are much lower than they would be for freshwater systems. The number of fish that you can hold depends on the species and the effectiveness of your filtration system.

  • Reef Systems:

Because invertebrates are more sensitive to organic matter than fish, stocking densities must be lower than in fish only marine systems.


Regular Maintenance


  • As stressed elsewhere in this care sheet, good maintenance is critical to the success of a Marine tank, as Marine Fish cannot tolerate fluctuations in water quality in the same that freshwater fish can. Regular testing, cleaning and appropriate feeding are vitally important.


However, as long as the tasks are performed regularly, the work is not overly time consuming. Prevention is better than cure, so follow these guidelines to ensure that your tank stays in top condition.


  • Daily:
  • Feed fish and check on behaviour for potential issues (health or territorial)
  • While feeding, perform a quick visual check to ensure that all pumps, filters and lights are working.
  • Weekly:
  • Test the water and adjust where necessary (only freshwater is necessary to top up losses from evaporation).
  • Clean algae from the front of the tank.
  • Check flow rates of filters and remove ‘scum’ from collection chambers of protein skimmers.


  • Every 2-3 weeks:
  • Perform water changes when nitrate levels get to the high end of tolerance range (see water parameters) if you do not have other methods of removing nitrates.


  • Every 6 months:
  • Change tubes or light bulbs on tanks containing corals, and globes in any UV units.