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Marine Water Chemistry

Marine water chemistry

Water testing using a test kit is something that should be done on all aquariums, freshwater or marine, but it is even more important with marine fish, which are not as tolerant to adverse conditions as some freshwater fish. The water we use in marine aquariums also needs to be of a higher basic quality, not just for the fish but also to prevent algae growth.

reverse osmosis unit

Source water

In a freshwater aquarium we can use conditioned tapwater for general community fish, but this is not suitable for marines. Although hardy marine fish would cope with tap water, it usually contains to many pollutants for delicate species, corals and inverts and is likely to cause problem algae to thrive. For marine fish the best source water to obtain is reverse osmosis (RO) water, which is as close to pure water as we can economically get. RO water can be either obtained from your local fish shop or produced yourself at home using a RO filter. Some retailers will even produce ready-mixed saltwater using RO. Over a long term basis it is more economical to produce your own RO water at home, for this you will simply need an RO unit, a mains supply to attach it to and a container for storing the RO water. Once you have your RO water, you can simply mix in the required amount of salt and you have a stored supply of good quality saltwater ready for your water changes.

Aquarium salt

Salt and minerals

Marine fish need salt and this is easy to obtain from your local fish shop. Good brands of marine salt will contain all the essential trace elements and minerals required by your fish and once added to your RO water, will be ready for the aquarium. The dissolved salt level, or salinity can be measured as 'specific gravity' using a hydrometer, which will tell you if your level is too high or low. Even if the water you add to the tank is the right specific gravity, the aquarium still needs to be tested on a regular basis using a hydrometer because salt levels can increase through evaporation of water, or 'salt creep'.

What to test for

As well as specific gravity and temperature, there are a number of properties and pollutants that need to be tested for in a marine aquarium. Many fish keepers tend to worry about water testing but it is a relatively simple process and can prevent serious problems from arising, as well as giving an indicator of the overall health of the aquarium. In a typical marine 'fish only' aquarium you should be testing for ammonia, nitrite, nitrate, pH, and phosphate on a regular basis. For 'reef' aquariums containing corals and inverts you may also need to test for copper, silicates, carbonate hardness and calcium.

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