What is wrong with my water?

The importance of good water quality in an aquarium cannot be stressed too greatly. Fish and plants are completely surrounded by the water, therefore any harmful compounds or sudden changes in the water quality will have an immediate and often drastic effect. Poor or incorrect water conditions are responsible for considerably more of the problems encountered by fish keepers than all of the other issues added together. In fact over 75{401015f8f8e2343b4069050f37ca81dccf45ad1a501f298b5d2086063e4e83fa} of fishkeepers troubles can directly, or indirectly, be related to water quality.

Recognising water quality issues.

It is obviously important to be able to recognize when water quality problems occur and understand how to overcome them. A very good indication of water quality troubles is if all of your fish, or all of a certain age or species, start showing signs of poor health over a short space of time. But how do we go to the next stage and identify which specific aspect of the water quality is causing the problems. The behavior or appearance of the fish no longer provides any reliable clues. Unfortunately many water quality problems affect the fish in a similar way – causing gasping, rubbing, rapid gill movements, lethargy or excessive mucous production,

Instead we need to rely on testing the water and some knowledge of what has happened in and around the aquarium in the days before the fish became unwell to give us an indication of what is happening.

Testing the water

Regular water testing is invaluable as it gives you an indication of what is happening in your aquarium and may enable you to detect problems before they affect your fish.

It is advisable to conduct regular water tests when you first set up your aquarium and again when you make any significant changes to the water, décor, filter or inhabitants. I would suggest ammonia, nitrite and pH are the essential tests. Water hardness, chlorine, nitrate and specific tests related to the fish you keep are also useful, but possibly used more selectively.

One word of warning with water tests – they only give you the reading in the water at the time that you test. New tank syndrome, where ammonia and nitrite levels increase as the filter bacteria develop can result in very short lived spikes in the concentrations of these dangerous chemicals. If you test the water once a week, the ammonia level may have been at dangerous levels for 5 days but be at acceptable levels when you actually test.

pH is also worth mentioning. In many cases it is not the actual pH that is the problem, but a sudden change. Discus, for example, can thrive in a pH of 6.0 or 7.5 if they gradually get used to such water. However if the pH suddenly changed from 6.0 to 7.5 it would kill them!

Testing the water as soon as you notice the fish are behaving unusually or have a changed appearance gives you a good chance of identifying the water problem

Recent events

Recent events often provide a clue to what may have caused the quality of the water to deteriorate:

If the aquarium is new or anything has been done which could impact the filter or the amount of waste that it has to cope with, you should suspect elevated levels of ammonia or nitrite. Adding new fish, over feeding, decomposing fish or plant material can all result in elevated levels of ammonia and nitrate as the filter bacteria try to decompose the additional organic waste material. Conversely, in a new aquarium or if the filter material is cleaned too vigorously, the numbers of filter bacteria will be insufficient to break down organic waste, and you will again get raised levels of ammonia or nitrite.

Water changes are another source of troubles. Tap water contains harmful chlorine and chloramine, which are severe irritants to the fishes gills and skin. Tap water may also be a different pH to the water in the aquarium – and if added in large quantities it can cause a sudden change in the pH resulting in the skin and gills of the fish becoming irritated.

Sometimes everything points to a water quality issue, but the tests show that conditions are ok. Remember here that the water conditions that impacted the fish may have been short lived, and you are testing when everything has balanced in the aquarium. Equally, the problem could be something that you aren’t able to test for. Toxins from sprays that have been used around the aquarium , or chemicals that are on your hands could result in the sudden onset of unhealthy fish. If your investigations don’t throw up an obvious answer, consider events that have happened in the few days before you noticed the fish were showing signs of poor health – it may give you a clue.

What to do?

The course of action will obviously vary depending on what is responsible for the fish looking unwell. Importantly you need to achieve two things. Firstly, correct the water conditions so that the fish are able to recover. And secondly, make sure that the problem doesn’t come back.

A good example here would be of high pH levels in an aquarium resulting from alkaline rocks in the decor or the gravel. This would irritate the skin and gills of the fish causing them to rub against underwater objects, jump at the surface and ‘yawn’ as they try to flush water over their gills. In severe cases it would also result in colouration changes and a build up of mucous on the skin and gills. A partial water change would help to lower the pH (assuming the pH of the tap water is lower). However the alkaline rocks are still there and would continually cause the pH to rise until it was removed or sealed with a suitable treatment.

Common causes of water quality problems and possible solutions.

pH Too high.

Cause. May be caused by tap water with a high pH, alkaline gravel and décor, limestone rocks in the water or cement.

Corrective action. If the tap water is not the cause of the problem and has a lower pH, undertake partial water changes to gradually reduce the PH. O.1 units every day is ok for most fish, but sensitive species may require a more gradual change. Remember to remove the offending item that is causing the high pH. If you are unsure, get two clean containers and add tap water. Measure the pH and add a reasonable quantity or gravel or the décor to one of the containers. Measure the pH in both containers after 3 – 4 days. They should be identical with any difference being due to the items you have added to one container.

If the tap water is the cause of the problem consider using RO water, adding a pH adjuster, or keeping fish that can survive in your local conditions.

pH too low.

Cause. Usually due to tap water or decomposing organic material. If you live in a soft water area, the tap water may be naturally soft and slightly acidic. Water supply companies may add buffers to the water to temporarily raise the pH (so it doesn’t eat away at old metallic pipework), but these can stop working after a day or so allowing the water to slowly return to its natural, more acidic condition. Using pH adjusters and buffers will help to correct the issue, but make sure that all future tap water is adjusted before it is added to the aquarium. Again keeping soft acid water species may be an alternative solution.

Organic material naturally releases acids as it decomposes (through the nitrogen cycle). If the water is very soft it can result in the pH lowering. Good aquarium or pond maintenance and the use of buffers will help to overcome the issue.

Ammonia and nitrite

Both should be close to zero in a healthy aquarium. High levels suggest there are not enough bacteria in the filter and aquarium to decompose the fish waste and organic material (leaves, food, dead fish etc) that are present.

Causes. There are a range of causes of elevated ammonia and nitrite levels including:

  • Newly set up aquarium
  • Newly set up filter
  • Overstocking with fish
  • Adding too many fish at one time
  • Insufficient or faulty filtration
  • Biological filter medium cleaned excessively or in tap water
  • Over feeding
  • Poor tank hygiene
  • Excess debris in the water.

Control measures include an immediate partial water change and removal of any excess debris followed by daily partial changes until the ammonia and nitrite are back to safe levels. Chemical additives can also be used to reduce ammonia and nitrite levels. In addition the cause of the problem needs to be identified. Avoid overfeeding and overstocking, ensure the filter is functioning effectively and don’t clean the media with anything that will harm the helpful bacteria.


Cause. High levels of nitrate are likely to occur in an aquarium through the tap water in some areas of the country, or naturally as the end result of the nitrogen cycle.

If the tap water contains high levels of nitrate, using Reverse Osmosis (RO) water either exclusively or to dilute the tap water will help. Alternatively commercial products are available that will remove nitrate. The natural production of nitrate can be controlled by encouraging healthy plant or algae growth, and by minimizing the production of nitrate by removing organic material before it starts to decompose, avoiding overfeeding and taking care not to overstock your aquarium.

Chlorine and chloramine.

Raised levels of chlorine and chloramine may be present in tap water as it is added to control living organisms and ensure the water is ‘safe’ for us to drink. Tap water can be made safe for fish and other aquatic organisms by leaving it to stand for 1-2 days with agitation (aeration or filtration). Alternatively, good quality tap water conditioners can be used to quickly remove both chlorine and chloramine – but do so before the water is added to the aquarium so that the fish don’t come into contact with it.

Unidentified water quality problems.

Sometimes the sudden onset of fish health problem points to a water quality issue. But even after testing and working out what has happened in the few days before it became noticeable, it is still difficult to identify exactly what has caused the problem. In these situations I would suggest that you check your tap water, to ensure there is nothing obviously wrong with it, and then conduct a 25{401015f8f8e2343b4069050f37ca81dccf45ad1a501f298b5d2086063e4e83fa} partial water change, removing any debris from the aquarium or pond. Treat the new tap water with a conditioner that includes colloids as these will coat the skin and gills of the fish providing extra protection from whatever is affecting the fish. Repeat this every 1 – 2 days for a week. Whilst doing this, remain alert and check with anyone who has been in the vicinity of the aquarium to see if they have any ideas of what could have caused the issue.

Water quality is a massive subject and this article has only touched the surface of some areas. There are many excellent books and web sites that can provide more details if you are interested.