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Distilled Water in the Aquarium and Quality of Water

Brief Description

This article is not only about benefits of distilled water for aquarium use, it's also about preparation and other ways of purification - we also have a forum under the article, so submit your experiences or questions there!


One of the major concerns of many fish keepers is keeping the water quality high for their fish and often we live in areas where the mains water is not to the best of standards. This can be very frustrating for us as no matter what we do by adding water conditioners and performing regular water changes, we seem to be fighting a losing battle as impurities are added to the aquarium each time we top up the tank or by just doing a standard water change. Many keepers have now turned to another method of providing better water for their fish by distilling the mains water.

Distilled water can be used for topping up the tank but when initially filling the tank vital minerals need to be replaced using commercial water revitalisers or the fish will not survive for any length of time, a low mineral count will also affect the growth rate of plants in the tank as they also need these vital minerals to survive and produce strong, healthy growth.

Some breeders or keepers of delicate fish will also use distilled water as they can then mix this with mains water or revitaliser to adjust the hardness of the water which in turn will affect the buffering capacity of the water, indirectly this will also affect the pH of the water as well.

There are also available some commercial salts that can be used to provide a balanced mix with the distilled water but if you are running a Salt Water tank do not confuse these with standard marine salt that is normally added.

What is the definition of distilled water?

Basically distilled water is mains water that has been boiled and the steam collected allowing it to cool and condense back into its liquid state. Large quantities of this water are produced commercially by industrial processes but producing small quantities is a very time consuming process. It is available to purchase in bottle form or in 5 litre tubs but preparing distilled water yourself can save you some money if you are prepared to spend the time going through the process. Below I will tell you a simple process of preparing your own distilled water if you wish to save a bit of money towards the running cost of your tank.

How do I prepare distilled water?

To save on costs preparing the distilled water can be undertaken by yourself. The basic process requires the water to be boiled and the steam cooled, most commercial cooler systems incorporate the use of a spiral tube made from copper tubing, this is not practical if the water is being used for the aquarium as many of the inhabitants will react badly to any traces of copper in the water. This problem can be overcome by using plastic or rubber airline to act as the cooler but unless you have the knowledge to create this apparatus there is another method. The water needs to be boiled to produce steam, place a large pan on a gas or electric stove to do this and cover the pan over with a tight fitting lid. The lid will act as a trap for the steam and the water will re-condense on it. Keep checking the lid and once droplets appear replace the lid with a second lid and repeat the process. Tilting the first lid will make the gathered distilled water run into a small puddle, this can then be tipped into a suitable container ready for use. Keep swapping the lids over until enough water has been collected for your requirements.

Key points to remember when using distilled water:-

Once the water is distilled it will contain no beneficial minerals or salts, it is alright to use this water when topping up the aquarium to compensate for evaporation losses but do not use this pure water for water changes or for filling the tank.

Distilled water will have a very low oxygen content, before using this water it must be aerated for a couple of hours or leave it for 24 hours standing in a suitable container to allow gaseous exchange.

The buffering capacity of distilled water is very low, it will need a buffering agent added back to the water to increase the KH so that there is no chance of any pH swings in the tank.

When storing distilled water keep it in a non-metallic container, metallic containers will over a period of time start to leach substances back into the water including some heavy metals.

Is there any other way of purifying water?

Yes there is, technically rain water can be classed as distilled water. Rain water is collected in the clouds as evaporated water from the planet surface, when it condenses it falls back to earth so theoretically it should be purified, there is however one problem with using rain water in the tank, depending on which area of the planet you live, there are varying degrees of pollution in the air that the rain water will absorb. In high levels of air pollution this can affect the health of your tank inhabitants.

Reverse Osmosis (RO) units are also available to purchase for treating mains water. They consist of pre-filters that remove minute sediments and heavy metals from the water before it is passed through a membrane where all of the other impurities are removed. These units were expensive a few years ago but now the price is much more economical for the hobbyist and are far more practical than using the standard distillation process.

De-ionisation is another process for purifying water. Cartridges contain special substances that pull away certain ions from the water and absorb them. The cartridges will need replacing on a regular basis as they get saturated with impurities and the compounds used can be expensive. They are often found nowadays sat on top of RO units as the final cleansing stage in the purification process.

In many areas, purification is not required for your tank water, check with the local water board to see how pure the mains water is coming through your tap.

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