Fish, Tanks and Ponds

Fish, Tanks and Ponds
A comprehensive guide to fish

Environmental problems

Ancistrus. Sp


We do have a tendency to make a big deal out of asking for some recent water test results whenever a problem occurs with a fish's health. The following pages explains why that is. Poor water quality or the wrong water chemistry are probably responsible for 90% of sudden fish illnesses or shorter than expected life spans, so the old saying "Look after the water and the fish will look after themselves" has a lot more truth in it than you might first think. Fish are not waterproof, their bodies are constantly fighting to keep the right level of salts while the surrounding water along with any pollution it contains is constantly invading their bodies. Keeping fish in poor water or the wrong type of water has serious consequences for the fish and usually results in a premature death. The symptoms exhibited by fish when the water is wrong often look like symptoms of other conditions or diseases, treating the symptoms will only have a very temporary effect and the ill health will worsen.


Ammonia is highly toxic to all fish, even at very low levels its effects can be devastating. Ammonia comes in two forms NH3 and NH4 and these vary depending on the pH and temp of the water. NH3 is the more damaging of the two and this occurs more at higher pH levels but this does not mean that NH4 (ammonium) is safe, both types of ammonia are dangerous and the only safe level for ammonia/ammonium is zero at all times.

The effects of ammonia poisoning include:

  • Irritation of the skin, eyes and gills.
  • Damage to the nervous system.
  • Damage to the internal organs.
  • Thickening of the gill tissue, making it hard to breathe.
  • Bleeding from the gills.
  • Ulcers.
  • Compromised immune system, leading to secondary infections.
  • Death.

Maximum safe level for ammonia - 0 ppm


Nitrite is almost as toxic to fish as ammonia is but it affects fish in a different way. Nitrite reacts with the hemoglobin in the fishes blood making it useless for its main job of carrying oxygen. Once this reaction has taken place it cannot be reversed and like ammonia poisoning there are a variety of symptoms depending on the severity of the nitrite poisoning.

The symptoms and effects of nitrite on fish are:

  • Lethargy.
  • Hypoxia.
  • Appearance of bruising.
  • Ulcers.
  • Compromised immunity.
  • Death.

Maximum safe level for nitrite - 0 ppm


Although widely acknowledged as being relatively harmless nitrate can still cause ill health or even death to aquarium fish. Ideally nitrate should be treated in the same way as both ammonia and nitrite by being kept as low as possible. Unlike ammonia or nitrite the best way to keep nitrate low is by making partial water changes using nitrate free water to replace water taken from the tank.

Excessive nitrate levels over lengthy periods may lead to:

  • Sterility.
  • Poor growth.
  • Algae blooms.
  • Osmoregulation problems, (pop eye or even dropsy).
  • Stressed fish which fail to thrive.
  • Compromise the immune system.
  • Lower the oxygen levels in the water.
  • Sudden changes in nitrate levels will cause the fish to go into shock, even if the change is for the better.
  • Fish have a varied tolerance to nitrate, some sensitive species will die with nitrate levels as low as 50 ppm.

The nitrate level should be kept as low as possible by making regular partial water changes, the level should be checked on a regular basis even when these water changes are being made on a very regular basis just to check that the amount and frequency of the water changes is sufficient.

Never let the nitrate level exceed 40 ppm for any fish.

Maximum safe level for nitrate - 40 ppm *


All fish have a pH range where they are comfortable and if gently acclimatised they can live quite easily a little out of their normal range in a lot of cases.

But keeping them a long way out of their normal range or by making sudden changes will result in the fish suffering ill health and an early death.

The by products left from the nitrogen cycle have a tendency to make the water more acidic, this will gradually lower the KH (buffering capacity of the water) until the water can no longer buffer the pH.

When this happens the pH will suddenly fall and cause the fish a lot of problems.

Symptoms of Acidosis and alkalosis:

  • Fish desperately try to escape from their water often by actually jumping out.
  • Hyper mucus production, mucus will be seen trailing from the fish.
  • The blood will be affected and the fish will be short of oxygen, made worse by the gills being covered with excess mucus.
  • The fins and tail will fray.
  • The fish may go into shock.
  • Eventually the fish will die.

If you discover that your fish have this problem don't be tempted to make a sudden change back to the ideal pH because doing so may make things worse by sending the fish into shock. Make all changes (not just pH) very slowly. pH levels should not be altered more than 0.3 in any 24 hr period. This doesn't mean change it by 0.3 in one go and then wait 24 hrs before doing it again, it means that make the 0.3 pH change in several small steps over the full 24 hrs. pH levels should closely match the ideal value for the species of fish being kept. Avoid problems by keeping fish together which require very similar conditions.

Other Pollutants

Ponds and aquaria can easily become polluted with all sorts of things if you don't pay attention.

  • Insecticide sprays, are just as deadly to fish as they are to insects both in the home and in the garden.
  • Cigarette smoke has some constituents which will readily dissolve in water and pollute it.
  • Aerosol sprays may leave a film over the water and lower the oxygen levels.
  • Mixing different remedies, this could lead to poisoning because some remedies contain copper and an overdose will kill the fish because copper is highly toxic to fish. The same thing may happen in a house with new copper water pipes.
  • Garden fertilizer could run into a pond after a rain shower, garden fertilizers usually contain an ammonia salt!
  • We usually think about the nitrogen cycle as starting with ammonia and ending with nitrate. In reality the process is far more complex than this and involves other organic chemicals being left over. All water will act as a solvent which means it will readily dissolve things, But it also has a limit to the amount of dissolved chemicals that it can hold, so the more pollutants that are dissolved in the water means that there will be less room for dissolved oxygen.

Make sure that you take all reasonable precautions to keep undesirable substances away from both ponds and aquaria. Bio-Marine Polyfilters will remove most pollution from water quite quickly and will retain it so that it can't leak back into the water.

A spare Polyfilter makes a very worthwhile addition to a fish keepers first aid kit because the sooner treatment begins the better the chance of a full recovery.

Changing conditions

Sudden fluctuations in temp or any of the above will lead to stress for the fish. Temp, pH and hardness of the water all affect the fishes internally.

Sudden changes don't give the fish enough time to adjust and its blood chemistry, digestion, kidneys and liver may not function properly and there will be a varying amount of oxygen available.

Small or unheated aquaria or small ponds which receive direct sunlight are the main offenders in this category.


Is easy, either keep species which suit your water or alter your water to suit the species that you keep. Then with good maintenance all these problems are avoided.