When preparing water for Discus it is inadvisable to simply de-chlorinate it, adjust the pH and use it. The fish may look fine but over a period of time various dissolved contaminates such as heavy metals, pesticides etc will have a detrimental effect on the health of your Discus. It is vitally important that you are able to produce enough water not just for regular water changes, but have enough in reserve for emergencies. Therefore relying on collecting rain water is "iffy" to say the least.

I recommend preparing tap water with either a Reverse Osmosis filter, a Heavy Metal filter or combination of both. What you need is dependant on the quality of your local water. We build a range of filters and have supplied them to most counties in the UK, feel free to contact us to discuss what you may need.

Today's tank bred Discus are kept in moderately hard water with out any problems all over Europe. It is only necessary to provide really soft water when attempting to breed the fish. The table shows the water parameters we work within.

The figures do of coarse vary from day to day and are shown as a guide only. Stability is important this can only be achieved by maintaining some carbonate hardness (Kh) or with the soft water, daily water changes. Domestic tap water will by and large have its pH adjusted by the water company to around 8, the Gh and Kh is dependant on the natural source of the water, the Gh can be as high as 30degrees, clearly unsuitable.

pH
The measurement of pH establishes whether the water has acidic, neutral or alkaline properties. It is measured on a scale from 0 to 14. 0 to 6.99 being acidic, 7 is neutral and 7.01 to 14 is alkaline. The scale is logarithmic so it is important to remember that 5 is ten times more acidic than 6 etc. The pH can be easily adjusted so long as the carbonate hardness is not too high by adding some type of acidic product such as API pH down. It is rare to increase the pH but this is achieved by adding some crushed oyster shell or limestone to the filter. Any pH adjustment carried out with livestock present must be done very cautiously. Large pH shocks over 0.5 can kill Discus.

gH
The general hardness, also known as total hardness of water is a measure of the dissolved calcium and magnesium salts present. The concentration of these salts directly influences the metabolism of fish, plants etc. Water with a high concentration of these salts is referred to as hard. We measure the Gh in degrees of German Hardness (dH) Excessive Gh can be removed with a Reverse Osmosis filter.

kH
The carbonate hardness, is also referred to as temporary hardness, is determined by the amount of carbonate and bi-carbonate salts present. This measurement is particularly important as the pH and Kh are interdependent. The Kh value is an indication of the waters natural buffering capacity. Moderate amounts will prevent fatal decreases in the pH level and excessive acidification of the water. We measure the Kh in German degrees (dkh) The carbonate hardness is always a proportion of the general hardness and any adjustments to the Gh will have an effect on the Kh.

GH (dGH)
Considered
Likely kH
Likely pH
Status
Water Change

0 to 2
Very soft
0
Under 6
V. Unstable
Daily 50%

2 to 5
Soft
1 to 3
6 to 6.5
Unstable
Daily 30%

5 to 10
Medium
4 to 7
6.5 to 7
Stable
X 3 Days 20%

10 to 16
Hard
8 to 14
7 to 8
V Stable
Weekly 20%

16 +
Very hard
14 +
Over 8
V Stable
Weekly 20%

Conductivity
Conductivity the measurement of the dissolved minerals and salts as ions, which conduct current through the water. Basically, the higher the ion concentration, the better the conductivity. Conductivity is measured in microSiemens. 33 microSiemens equates to approximately 1dGh, or 17ppm.

Discus in a show tank can be kept quite happily in water with conductivity values of around 800 microSiemens, indeed young Discus will positively benefit from mineral rich water. If your goal is to breed Discus then you will only succeed where the conductivity measures less than 100 microSiemens. Discus will spawn in hard water, but the osmotic pressure generated by a high mineral content will destroy the eggs.

Article author Hans from Discusvis.nl