Behaviour of fish
Abnormal behaviour after introducing new fish or plants
Refusing food, feeding, food
Mating and breeding behaviour
• What is the easiest way to keep discus fish?
Buy only our STENDKER discus fish and continue to feed them with out STENDKER discus feed. Do not add other fish later (except for STENDKER discus fish).
•How often should I change the water and how much?
This depends to a large extent on how many fish you keep and how much you feed. The water should be changed at the latest when the nitrate level rises above 100 mg, the pH value drops below 6 or when the fish feel uncomfortable. Generally you should change 10-20 % of the water every week or 30 % of the water every two weeks.
•How often should I measure which water values?
pH value should be measured once a week. Normally the pH value is above 7. If the pH value should drop below 6 as a result of feeding and a very good filter, change the water. If the value is still around 7 after one week, you can delay changing the water by one week.
Nitrate should be measured once every two months (before changing the water) if the filter is functioning well.
Ammonium, ammoniac and nitrite should be measured daily for new aquariums until the filter reduces these values to practically zero when feeding normally. Thereafter these values need only be measured if the fish display unusual behaviour.
•I am planning to go on holiday. How can I look after my discus fish during this period?
See our detailed tips under the heading "What to do when on holiday". A fast is better for your discus fish than killing them by well-intentioned over-feeding by your neighbours.
•Small bubbles formed when changing the water and my fish are dying. What can I do?
If you run the water through a hose under too much pressure into the aquarium, small bubbles will form. You can avoid bubbles forming by fixing a shower head to the end of the hose. The problem is that these bubbles not only settle on all objects in the aquarium but also in the gills of the fish, causing breathlessness in the fish, and often result in suffocation. The only way to avoid this is to place the fish temporarily in a bucket (which does not contain remains of cleaning agents) or in another aquarium without bubbles (duration: not more than 20 minutes without aeration). The fish can remain in a bucket for several hours without a problem if you add an outlet stone.
• The fish gills are noticeably scraggy and frayed. Why is that so and what can I do about it?
This can occur in older fish (older than 2 years). We recommend taking the fish out of the tank, placing it on a damp towel and carefully cutting the gills with nail scissors. This process is similar to cutting nails on humans and does not hurt the fish. Be careful to cut only the straggly part of the gills.
• Can I mix different types of discus fish?
You can mix different colours from the same breeder at any time. However, you should never mix different types such as fish caught in the wild, fish from Asiatic breeders or STENDKER discus fish because fish from different breeding operations will have different microbial strains and therefore may not be mixed.
•I had Asian discus fish and would now like to change to Stendker discus fish. What should I do?
Disinfect the complete aquarium including filters and accessories (such as nets, glass scraper, suction hose, etc.) using hydrogen peroxide (0.5 litres of 33 % hydrogen peroxide to 200 litres of aquarium water for 24 hours). Then change 100 % of the water and run in the filters again before adding STENDKER discus fish to the aquarium (see also preparing the aquarium).
• My tank fills up with algae very quickly. Why is that so and what can I do about it?
It may be a question of too much daylight or too much artificial light. Try to reduce the light source. It can also be caused by too high phosphate levels from feeding. Reduce the amount of food and change the water more often.
•Where have all the snails come from and what can I do about it?
Snails and their spawn are often introduced into aquariums through bought fish or plants. Remove all visible snails to keep the numbers down. Freshwater puffer fish should help since they feed mainly on snails.
•How long should I keep the light on in the aquarium?
The light in the aquarium should be switched on for around 12 hours. You can set this using a timer used only for the light and which operates independent of the pumps and heating rod. At night we recommend a night light so that the fish can orientate themselves and are not so startled by every noise when sleeping.
•How long do discus fish live?
If cared for well, discus fish can live to be 15 years old.
• How large can discus fish grow?
The largest discus fish we ever bred was 22 cm long. The average is 16 cm. Individual fish can reach 20 cm diameter.
How many discus fish should I put in my 300 litre aquarium so that they can all grow up healthy? I would like to buy fish 8 cm in size.
We recommend at least 25 discus fish so that they develop assertiveness when feeding as well as good feeding and group behaviour.
•How can I recognise healthy, well-grown discus fish?
You can recognise a healthy, well-grown discus fish by its clear red eyes and circular shape. Look at the discus fish from the front. The fish should not taper above the eyes (forehead) because that is where the fat reserves of the discus fish are stored. Observe its feeding habits. If it eats fast and greedily it is healthy.
Behaviour of fish
•In my 300 litre aquarium I have 10 fish of 8 cm in size and one fish is being bitten by the group and is losing weight. What can I do and why is that?
Discus fish belong to the perch family and display the group behaviour described by you, as all other perch, when the group is too small. For a 300 l aquarium we recommend at least 24 discus fish of 8 cm to ensure harmonious coexistence and prevent one fish being driven away from the food. You should reduce the group slowly as they grow until you end up with c. 15 fully grown fish which feel comfortable in your aquarium.
•A discus fish has become aggressive in my aquarium and is biting the other fish. What can I do and why is that?
Probably the group is too small. Such aggressive behaviour is extremely rare in larger groups of discus fish (1 fish per 15 litres of water).Probably the group is too small. Such aggressive behaviour is extremely rare in larger groups of discus fish (1 fish per 15 litres of water).
•Today individual discus fish have suddenly started shooting around the aquarium. Why is that so and what can I do about it?
Most probably the water is highly contaminated. Measure the nitrite level. If the
value is extremely high, immediately change 90 % of the water. If the nitrite
level is zero or low, filter via activated carbon to remove possible toxins from
the water. It is essential to remove the activated carbon bag from the aquarium
after 2-3 weeks since the absorbed toxins will be released again into the water.
You must do this as quickly as possible; if not, the fish will die of poisoning
after 24 hours. If the cause is nitrite poisoning stop feeding until the levels
return to normal.
•Two of my discus fish have suddenly become aggressive and are biting the other fish. Why is that so and what can I do about it?
Probably these two fish are a pair and want to lay their eggs which is why they are claiming the larger part of the aquarium as their territory. You can either increase the number of fish (5-6 fully grown discus fish per 100 litres) or remove all other fish from the tank so the pair has the opportunity to rear their young successfully.
•Can I mix different colours and sizes of discus fish in one tank?
Yes indeed, as long as you take care to introduce fish from the same breeder.
•My discus fish go up almost to the surface and open their gills and leave them open. Why is that so and what can I do about it?
Probably there is an acute shortage of oxygen. Check if the filters are functioning properly, measure the ammonium, ammoniac and nitrite levels. If one of these levels is very high, immediately change 90 % of the water in the aquarium and stop feeding until the levels have returned to normal. If there are remains of food on the bottom, it is essential to remove them (increased nitrite levels). These water values prevent oxygen being absorbed by the fish.
•When the light goes out at night my fish remain motionless at the bottom of the tank. Why?
Discus fish sleep too. Please be quiet and do not frighten the fish. Add a small night light as a substitute moon and leave your discus fish to sleep.
•After changing the water my fish start shooting around the tank.
Most probably the water is highly contaminated. In spring slurry residue often seeps into the groundwater through over-fertilisation and from there into the domestic water system. We recommend filtering with activated carbon to remove the toxins from the water. It is essential to remove the activated carbon bags from the aquarium after 2-3 weeks.
•One of my discus fish swam very quickly against the glass pane and next day I found it dead. How could that happen and what can I do about it?
Probably it was simply frightened, e.g. it was disturbed during its sleep phase or by the light being turned on and injured itself fatally (e.g. fractured skull). We recommend leaving a night light on for the fish.
•One fish is quite dark and colourless and remains next to the filter. Why?
Probably it is being pushed away from the food by the other discus fish and so is the weakest in the group. It is trying to avoid the aggression of the other fish by hiding. There are two things you can do: 1. A temporary solution would be to place the fish in a separate aquarium and feed it intensively at 33 °C and nurse it back to health. You can put the fish back in the aquarium after c. two weeks. It will be able to assert itself in the group with renewed strength. 2. You must expect another fish to be bitten by the group and kept away from the food in the near future. You can prevent this by increasing the number of discus fish in your aquarium (to 10-12 fish for an aquarium of 180 litres).
•I went on holiday and my neighbour fed the fish. When I came back all the fish were dead. Why?
Probably your neighbour fed them too much because the fish looked so hungry and ate so greedily. The filters couldn't cope with the increased amount of food, nitrite formed and since the amount of food was still too high, the filter system collapsed completely. Most likely your discus fish died of nitrite poisoning or lack of oxygen. We recommend you leave your fish to fast when you go on holiday. That is good on occasion for humans and animals.
•The fish in my cellar hide when I come. Why?
Probably no one is in the cellar for must of the day so that the fish see your presence as an intrusion. You can prevent this by pretending to the fish that someone is in the room the whole time, e.g. by leaving the radio on.
Abnormal behaviour after introducing new fish or plants
•I bought a new discus fish and added it to my other fish. Three days later all the others started to die but the new fish appears healthy. Why?
The new fish is probably from an Asiatic breeder and has a microbial strain or has introduced one and your discus fish could not cope with it. In such cases go to the vet and ask for antibiotics (e.g. Neomycin or Nitrofurantoin) and start the treatment immediately. (You will find recommendations for treatment on page 7).
•We bought companion fish (not discus, neons). After c. one week our discus fish died and only the neon fish survived. Why?
The companion fish introduced a microbial strain into the aquarium which your discus fish were not used to. Without antibiotics, the immune system of the fish couldn't cope. Probably dark coloration could be observed on the discus fish by the third or fourth day; treatment with antibiotics (e.g. Neomycin) would have had to have started at this point. We do not recommend adding further discus fish.
•We bought companion fish (not discus, neons). The discus fish are still alive but all neon fish died after 2-3 days. Why?
Probably you took your time in adjusting the water for the fish in order to do it really thoroughly. After opening the fish bags you should put the fish in the aquarium within 15 minutes. We assume the neon fish died from a lack of oxygen.
•I bought plants from an aquarium stocked with fish. Four days after putting the plants in my aquarium my fish turned dark and flattened their fins. Why is that so and what can I do about it?
Probably your introduced a microbial strain into the aquarium with the plants. Your fish are reacting to this unknown bacteria. We recommend using antibiotics, e.g. Neomycin or Nitrofurantoin, to stabilise the fish.
•I added a new type of discus fish (yellow) to the group. All the fish died and only the yellow discus fish survived. What can I do?
The yellow discus fish is from an Asiatic breeding operation which you probably mixed with fish caught in the wild or with our STENDKER discus fish. The different microbial strains caused the death of your discus fish. This might have been prevented by treatment with antibiotics if begun early enough.
•I have scalar fish and have added a small group of discus fish to the tank. Unfortunately many of the discus fish are stunted in their growth although all fish feed well. What can I do?
Your scalar fish probably have tape worms. These tape worms have infiltrated the
discus fish and the result is stunted growth. We recommend treatment with
Droncit. Dissolve one 50 mg tablet for 100 litres of water in the tank; after 3
days change more than 50 % of the water or filter using activated carbon for 24
hours and repeat the treatment on the fourth day.
Refusing food, feeding, food
•I added large new discus fish (more than 15 cm) to my aquarium and the fish have not eaten for a whole week. What should I do and what is causing this behaviour?
Adult discus fish need time to adjust to a new environment and often wait for three to four weeks before eating. To encourage the appetite of the fish it is useful to have a couple of smaller discus fish in the aquarium who eat well. Another option is to raise the temperature to 33 °C after three weeks and hence increase the metabolic rate and the appetite of the fish.
•My STENDKER discus fish have stopped eating. They are breathing quickly and heavily. Why?
The probable cause is either poisoning or a lack of oxygen. Check the nitrite level, the pumps and the outlet stone. If the nitrite level is very high, change 90 % of the water immediately. If everything is in order, filter for 2-3 weeks using activated carbon to remove possible toxins from the water. Remember to remove the activated carbon bag after 3 weeks at the latest, otherwise the toxins will be returned to the water. You must act immediately because the condition of your fish will deteriorate with every hour and can even result in death.
•My discus fish have stopped eating. However, their breathing and behaviour is normal. Why have they stopped eating?
We recommend raising the temperature to 33 °C to increase the metabolic rate of the fish. Wait until they have been eating well for several days and their excrement has turned dark for at least two days before dropping the temperature back to its normal level (29-30°C).
•My fish aren't eating properly. Why?
It could be the food. Try our STENDKER discus food. Also check the temperature of the water which should be between 29-30°C. In addition you may not have enough fish in the aquarium which reduces their assertiveness over food and lowers their appetite.
•My fish spit their food out. Why?
Perhaps they don't like the taste, it is too hard for their soft mouths (e.g. granulate) or perhaps the food is new and unfamiliar. Sometimes the fish only play with the food because they are not hungry. In that case you should feed less.
•How often and what should I feed?
We recommend feeding our STENDKER discus food (as a wholesome all-in feed) three times a day.
1 x in the morning (1 hour after switching on the light)
1 x at midday (preferably always at the same time)
1 x in the evening (2 hours before switching off the light)
The discus fish get used to regular feeding times and will be waiting for you. This means you can quickly feed them by hand (of course without cream and soap on them).
•My discus fish are c. 1 year old and are between 10 and 12 cm in size. Why aren't they growing properly? I give them varied food: granulate, artemia and mosquito larvae.
Your feed consists more of titbits and is not enough to ensure healthy growth. We
recommend feeding our STENDKER discus food three times a day because it contains
everything a discus fish needs (vitamins, minerals, trace elements and above all
protein). It can't be simpler or more efficient than using our food mix for your
discus fish. |In the course of 45 years we have worked continuously con refining
the composition and continued to optimise our feed mix. Utilise our experience
and use our STENDKER discus feed which you can buy in pet shops.
•My discus fish are getting small white spots on their skin. Why is that so and what can I do about it?
You can treat the fish with a salt bath. Take 15 litres of water from the aquarium and put it in a clean bucket (not a bucket used for cleaning) and dissolve 500 grams of iodine-free table salt in it. Put the fish with spots in this solution for a maximum of 30-60 seconds. Then return the fish immediately to the aquarium. All ectozoons on the mucous membranes will remain in the salt solution and the immune system of the fish will be better able to deal with the parasites remaining in the aquarium. Do not leave the fish during treatment to answer the telephone or for other distractions otherwise they will die.
•We introduced new discus fish to the aquarium yesterday. Today the fish have a white edge to their fins. Why is that so and what can I do about it?
When catching the fish the mucous membrane, particularly on the edge of the fins, was damaged slightly. This makes the fin edges turn white. Add some water purifier (e.g. Aquasafe) to the aquarium to lower the harshness of the water. The problem with the fins should resolve itself in two to three days.
•Which medicine do you recommend for gill worms and where do they come from?
We recommend FMC for gill worms. It comprises 1 l formalin + 3.7 g Methylene Blue + 3.7 g Malachite Green (all available from your chemist). Add 3-4 ml of the mixture to 100 litres of aquarium water and after c. 10 seconds change 90-100 % of the water. Repeat this treatment after exactly four days. The gill worms should be much reduced by then. However, gill worms cannot be eliminated completely.
•Which medicine do you recommend for white excrement and what does this signify?
We do not recommend using medicine for white excrement; you should raise the temperature to 33 °C for c. 10-14 days. this will raise the metabolic rate of the fish and will improve feeding habits and their digestive system. In turn this will strengthen their immune system and the excess intestinal parasites will be excreted naturally.
•How can I recognise a bacterial infection and what should I do?#
bacterial infection generally occurs three to four days after adding new fish to the aquarium. The infection causes the colours of the fish from the original stock to turn dark, lay back their fins and withdraw to a corner of the aquarium in a cluster. In this case unfortunately you must use antibiotics (e.g. Neomycin or Nitrofurantoin) which you can get from your vet.
•My fish are rubbing themselves. Why?
The fish probably have an infestation of ectozoons. In this case we recommend
placing the fish once in a salt bath. Take 15 litres of water from the aquarium
and put it in a clean bucket (not a bucket used for cleaning) and dissolve 500
grams of iodine-free table salt in it. Put the fish with spots in this solution
for a maximum of 30-60 seconds. Then return the fish immediately to the aquarium.
All ectozoons on the mucous membranes will remain in the salt solution and the
immune system of the fish will be better able to deal with the parasites
remaining in the aquarium. Do not leave the fish during treatment to answer the
telephone or for other distractions otherwise they will die.
Mating and breeding behaviour
•My discus fish pair is laying eggs and is becoming aggressive towards the other fish. Why?
This is normal breeding behaviour of discus fish; they are protecting their territory. If you want to breed young fish you should remove all other fish from the aquarium and keep this one purely as a breeding aquarium. If you simply want a peaceful discus tank, increase the stock so that territorial behaviour cannot develop (5-6 adult fish to 100 litres of water).
•How can I get my discus fish to lay eggs?
Put a group of 4-5 fish in an aquarium of 200 litres and change more than 50 % of the water. Changing the water will lead the fish to believe the rainy season has started and instinctively they will start to lay eggs.
•My discus pair always eats the eggs. Why?
Lower the water temperature to 27 °C. This lowers the metabolic rate of the fish and at the same time increases their protective instincts to the eggs.
•The other discus fish always eat the eggs from the breeding pair.
You can only avoid this by removing the other discus fish from the aquarium or separating the pair from the group.
•My breeding pair are laying eggs but on the first day the eggs turn white. Why?
The water in your aquarium is too fresh and too harsh. You can alter that by changing the water less and adding a water purifier to the aquarium each time you change the water.
•My breeding pair are laying eggs but the eggs remain transparent and no babies are born. Why?
Either you have two females who have laid eggs together or the male is still too young to fertilise the eggs.
•Why do my discus fish eat the baby discus fish?
Either the clutch is too small (less than 50 fish) so the parents eat the young fish in order to make room for a larger clutch. Alternatively, the parent fish were unsettled by the water being changed or another disturbance which made them eat the babies.
•How long should I leave the baby fish with the parents?
t least 12 days, although 3 weeks is better. On the 5th day after they hatch you should start adding live artemia to the skin secretion of the parents.
•A red and a blue discus fish are laying eggs. What colour will the babies be?
Probably 20 % will be red, 20 % blue and 60 % red ^ blue striped pigeon