How To Keep Discus Fish

How To Keep Discus

How to keep Discus fish or any fish begins with the correct water parameters. With this in mind Chris Ingham explains the importance of the correct water conditions, and how best to achieve them. A visit from a customer today has prompted me to write this article, so Mark from Plymouth this ones for you. Not just because of this one visit, but I seem to be explaining this subject every single day to many others. So I thought it worth covering this month. The main problem being understanding correct water conditions or parameters of the water needed to support our aquatic life. To all who understands the nitrogen cycle and already understands the importance of this subject please bare with me and it doesn’t hurt to keep up to date any way. To those who don’t, please take note. Our fish are kept in a closed system, this means a glass box of water that they have to live in, feed in and excrete in. It would be like us living in a sealed room slowly filling up with toxic smoke, we would not like it and when dangerous levels are evident, we would become ill or diseased. This is what happens if water changes and the correct water management are not carried out on a regular basis. So we now realize that the water in which these animals live in and are at our mercy must be controlled in a specialized manner, according to the species of fish that are kept.


The principle of biological filtration is to build up in sufficient numbers a colony of friendly bacteria to break down the waste (ammonia) from the fish into less harmful nitrite and then nitrate, this is known as the nitrification and denitrification process. This process is known as the nitrogen cycle. To explain the waste products or fish excretion from the fish will give off ammonia in the water and obviously if not diluted down will increase and would not be pleasant for the fish who have to live in it. This is where a good biological filter will do wonders for any fish tank, not just discus. First of all the filter must be mature and house good friendly bacteria (such as nitrosomonas sp) in enough numbers to deal with the job ahead, and that is to break down the ammonia into less harmful nitrites (NO2). But this is still harmful to the fish, so then the biological filter will break this down further into nitrate (NO3) which will not harm the discus. This is why a good adequate filter is needed for any aquarium not just discus but for any fish, although some fish are more resistant to it than discus which will only tolerate ammonia for short periods. Goldfish for example will tolerate ammonia as high as 500 ppm with discus only tolerating 20 ppm. Good water changes on a regular basis will help to reduce the nitrate levels which if allowed to reaching high levels will contribute to algae growing over your plants, rocks and the sides of the tank. Strong sunlight or lights left on for extended periods will also have an effect on ugly algae also.


PH is measured on a scale of 1 to 14 and 7 are deemed as neutral. Below neutral is acidic and above 7 is alkaline. For discus keeping the best perimeter is 6.5, but baby discus will benefit from higher levels up to 7. This is another area where a lot of confusion and conflict has broken out. Discus being easier to keep than most people think will in fact accept quite a wide range of PH value. Some customers of mine keep their discus at 5.8 with no problems, while others at 7.2. It’s just that 6.5 has been the best PH value I have found to hatch discus eggs in the past and has been accepted by many breeders as the best reading of PH for general discus keeping. Sometimes you may need to adjust your PH up or down. Be very careful when using buffers, many can contain phosphates which will do no favours for your discus. The best one I have found to use is made by API and they make a PH buffer that is for up and down and contents no phosphates. A good accurate way of measuring PH is with a digital meter, these are by far more accurate than liquid test kits as recent test have proved. GH is the general hardness of the water. The more dissolved minerals and salts in the water, the harder the water will be, giving a higher reading of GH. When measuring GH any readings under 10 is deemed as soft water and fine for keeping discus in, although my perfect figure is 3. Above 10 and that is classed as hard water. Again discus can be kept in a GH from nearly zero to as high as 18 or 19 (but don’t expect them to breed at this end of the scale) As with the PH testing digital meters are a lot more accurate than liquid test kits and are very cheap to buy these days. So there we have it, a good under standing of how the water parameters need to be for successful discus keeping. I could go deeper into this subject but this is the basics that need to be adhered to for now. Those of you that venture into breeding etc will need to learn all about osmosis and the concept with water hardness. It is well worth under standing the nitrogen cycle and how it works. Your fish will be very grateful too.


  • Sometimes discus will do a mad dash about the tank, do ammonia test. High levels of ammonia can burn the gills of the fish and make them literally jump out of a tank to get away from the pain.
  • Plenty of aeration will do wonders not only for your fish but the filter system will greatly benefit it too.
  • If plenty of oxygen is present in the water aerobic bacteria will form. This is the most efficient bacteria to break down ammonia.
  • Trickle towers are the best form of filtering water for aquatic use because they will house millions of oxygen rich aerobic bacteria.
  • Be careful when using chemicals, over dosing can wipe out the friendly bacteria in a filter system and cause massive problems with your fish.

Chris Ingham

Author of Discus World, the complete up to date manual for the discus keeper.