References - Water for Discus
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Water for Discus

Mary Ellen Sweeney


Discus are not really difficult to keep . . . as long as you do what they want! What discus want is: excellent water quality, free of toxins like chlorine, ammonia, nitrite, phosphate, etc.; correct water chemistry, pH and water hardness; and proper temperature, between 82 and 86F. Excellent water quality is provided by your three-part filtration system and one-part water changing system. Water chemistry is tested and determinations are made for adjustments. The water should be soft, between 3 and 15dH. The pH should be between 5 and 6.5. This is where most discuskeepers have trouble. Discus would prefer not to compromise on these values. To believe that you can acclimate discus to harder water or to higher pH levels or lower temperatures is folly. The discus may live, may breed even, but they are living and breeding under stress. In fish, as in humans, stress shortens their lives and makes them more susceptible to disease. Strive for the ideal rather than trying to cheat the system.


You can probably walk into any pet shop and find out what the general water conditions are in your area. That would be fine if you were trying to decide whether to keep guppies or angelfish in your community aquarium, but it will not do for discus. You will need to test your water as it comes from the tap and continue to perform periodic tests to ensure that your aquarium water is up to par and within proper range for a number of values.

Testing the Waters

You should initially test for chloramine and chlorine, pH, and alkalinity. Once the levels of pH and alkalinity in your raw water have been established, you can decide how you want to handle the situation. Some raw water is just about perfect for discus with little or no modification. Some water needs extensive conditioning before the first fish can be introduced. Once you know these values, you may decide you want to keep another kind of fish! After the initial battery of water chemistry tests, you should continue to test the above, certainly after the first few water changes, and add a few more tests to the list: nitrite and nitrate, phosphate, and in the planted tank, iron and CO2. Simple, isn't it? Test kits have become very user-friendly in recent years. All these tests can be researched in a good chemistry book and the reagents assembled through chemistry supply outlets; however, the test kits and probes available for the aquarium hobby are generally inexpensive and easy to use.

Toxins in the Water Supply

The water company can be your friend or your foe. Chlorine or chloramine are routinely added to the water in many parts of the world. A simple color test kit will determine the presence and concentration of either. Removal of chlorine or chloramine is part of the process known as conditioning your water. There is more than one way to skin a cat, and there are many ways to condition your tapwater. Conditioning is the process of adjusting the chemistry of the water to bring it into line with the requirements of the fishes you are keeping. Chlorine is readily removed from tapwater by activated carbon prefiltration, aging the water, or permitting contact of the water with the air through the use of a spray. Chlorine can also be removed by adding prepared chlorine removers. If you are conditioning your water with reverse osmosis or deionization, these processes remove virtually all toxins (and a lot of necessary elements as well, that must be replaced), but more about reverse osmosis and deionization later. Chloramine is a combination of chlorine and ammonia, and some water companies need to use this for disinfection of the water supply. Chlorine is not good for fishes and chloramine is worse. If your test reveals chloramine, be sure to use a water conditioner that is chloramine specific. Aeration will not remove chloramine.

Water Hardness and Alkalinity

It may be that your water hardness and alkalinity are perfect for discus but unfortunately this is not always the case. It is far easier to adjust hardness and alkalinity upwards as when keeping hard-water fishes, but lowering these values is by no means impossible. It simply involves another step in the water conditioning process. Total hardness (general hardness) is the sum combination of carbonate and noncarbonate hardness of your water. Total hardness is measured as, degrees, dH, or ppm (parts per million). One dH is 17.9 ppm. How total hardness is expressed depends upon the author and his orientation. I prefer dH simply because as a discuskeeper, I like to see smaller numbers when I am measuring water hardness! If I were keeping African cichlids I might prefer to measure my water's hardness in ppm. Total hardness is usually not a big issue in keeping discus; alkalinity is a far more important factor in the breeding of discus. Alkalinity is sometimes referred to as carbonate hardness(KH)or buffering capacity. Alkalinity is the important factor in breeding discus and controlling the pH of the water. Alkalinity refers to the level of calcium, carbonate and bicarbonate in the water. It is measured in KH or mg/L CaCo3 or parts per million. One milligram per liter (mg/L) is the equivalent of one part per million. Soft water is 3dH and 0 to 50 mg/L CaCo3; medium soft water is 3 to 6 dH and 50 to 100 mg/L CaCo3; slightly hard water is 6 to 12 dH and 100 to 200 mg/L CaCo3; moderately hard water is 12 to 18 dH and 200 to 300 mg/L CaCo3; hard water is over 18 dH and over 300 mg/L CaCo3. The values for general hardness and alkalinity given above do not always match each other. It is entirely possible to have a higher reading of general hardness and a lower reading of alkalinity. The lower reading for alkalinity is the more desirable for discus water. Discus will do quite well in slightly to moderately hard water. In fact, many breeders routinely keep their fish in these values to ensure proper development of the young fish, but for development of the eggs, soft to moderately soft water, particularly concerning alkalinity is critical. Therefore, it is not necessary to drastically adjust the general hardness or alkalinity when you first start to keep discus unless the values are very high.

Reducing Water Hardness

It is best to test the pH and alkalinity of your water before making any investments in reverse osmosis or deionization equipment. As long as the general hardness and alkalinity are in the ranges mentioned above, you should have no trouble. Driftwood and peat will both contribute to softening of the water. You may find that your slightly to moderately hard water will respond very nicely to the introduction of a piece of drift wood and a bag of peat in your filter! Beyond this, or if you are at the stage where you are seriously considering breeding your discus, you can look into reverse osmosis or deionization pretreatment of your water. Both of these methods remove all trace of water hardness and a very high percentage of the impurities in the water, through extremely fine straining action in the R/O and specific resins in the DI. Water that has been handled in this fashion is stripped of necessary trace elements and must be reconstituted before use in the aquarium. Reconstituting salts are available commercially. Some authorities recommend mixing the water with 5% tapwater, but if your tapwater contains toxins, this is not the best method by any means. Household water softeners used in many homes are entirely unsuitable for preparing water for discus. The resins in these units exchange hardness ions for sodium ions and additional sodium is contraindicated in keeping discus.

About pH

Discus are very particular about pH. Keep your pH below 7 and above 5.5. The ideal pH for discus is 6. At pH levels above 7, discus are stressed. Below 5.5, the pH is inclined to plunge rapidly, so I find 6 to be comfortable for both the fish and the fishkeeper. Alkalinity and pH are closely related. Hard water naturally tends to be alkaline. Soft water naturally tends to be acidic. This is because of the buffering capacity. Buffering capacity represents the presence of alkalinity (carbonate hardness) and the ability of the water to maintain high pH. It is a chemical balancing act. Just enough carbonate hardness and the pH remains at the desired level, too much carbonate hardness and the pH will remain high, too little carbonate hardness and the pH will crash. Maintain your carbonate hardness at around 10 or 15 dH and you should have no problems with pH. Check your pH with every water change until you are able to get a feel for how your water behaves. If you notice that the pH drops quickly, you must add back carbonate. If your pH resists change to lower values, you must remove carbonate. There are many methods of lowering your pH, most with some form of phosphoric acid, from drops to powders, but one of the gentlest and safest methods is through the use of peat moss. Because the peat adsorbs carbonates and acidifies the water, you should be able to maintain desirable pH and carbonate levels through the use of peat alone.



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