Water: the essential element for fish

The texture of good quality water is subtle

Water: the essential element for fish

The texture of good quality water is subtle
The texture of good quality water is subtle

On a very basic level water is 99.98% H2O in a liquid that your fish swim, eat, breathe and excrete into. What about the other .02%? Is it important? Of course it is. It is these minute quantities of dissolved gases and dissolved solids that makes all the difference in whether the water is hospitable or poisonous to the fish. It is this 0.02% of dissolved substances that make sea water, river water and lake water different from each other. Note that seawater has a much higher level of dissolved salts of around 3.5%. It only takes minute quantities of the common gases such as ammonia, carbon dioxide or insufficient oxygen to poison or drown fish. Likewise it only takes a small amount of pollution or the wrong type of chemical to be dissolved in the water to poison and kill fish. But when conditions are just right or within reason then your fish will thrive without much care from you.

Creating a generic biotope for your fish to live in

The most common elements of an aquarium biotope
The most common elements of a biotope

As a fish keeper is is your responsibility to recreate a reasonable biotope for your fish that is as close as possible to the fish’s natural environment as you can.

Water has dissolved gases such as oxygen, carbon dioxide, nitrogen, ammonia and chlorine. Some of these gases are poisonous while others are necessary for fish to breathe. Water also contains dissolved minerals that determine the general hardness of your water. Some fish thrive in very hard water with a high ph, while other fish prefer much softer water with a lower ph. Organic matter can also dissolve in the water, usually darkening the water and acidifying it.

A biotope should include a substrate, plants and a source of light with the temperature of the water kept within a suitable range for the plants and fish. The choice of subrate includes gravel, sand, and even soil. Soil is usually topped with gravel. Other less essential features you might want to include in your fish’s biotope could include rocks, roots and branches.

The Lake Malawi Biotope explained here

The Amazon Biotope explained here

Is tap water safe for fish?

Is tap water safe for fish
Is tap water safe for fish

Tap water direct from the tap is not suitable for use in an aquarium. The main problem is chorine which water companies put in the water to kill off any potential bacteria in the water. To remedy this you need to leave your tap water standing in a container for at least 24 hours. This allows the chlorine to evaporate. This can be achieved by using buckets of water or water barrels to store the water.

Another danger to your fish is from dissolved copper which can come from copper pipes. Water that comes into contact with copper will slowly absorb the copper. This problem is worse for new copper pipes. But this can be remedied by running your tap water for a few minutes until uncontaminated water starts to come through. Copper is poisonous and even copper coins left in your aquarium will slowly dissolve and kill your fish.

If you are going to be serious about the quality of your fish’s water then you should buy a water test kit. A good test kit will test ph, ammonia, nitrite and nitrate as well as general hardness.

If you are a new fish keeper who wants the best chance of keeping your fish healthy and alive then test your tap water before you buy any fish. When you know the ph and hardness of your water then you can buy fish that prefer the water from your tap. Adjusting your water to suit fish that like a different type of water is best left to the advanced aquarist who don’t mind the extra effort. Some fish when kept in the wrong type of water will simply die after a few weeks and certainly won’t thrive.

If you are a more experienced aquarist then you can start adjusting the ph and hardness of your tap water so that you can keep the more delicate species of fish. To soften your water you can buy a reverse osmosis device that will remove the minerals from your water. Such water is usually too soft and must be mixed with unfiltered tap water to achieve the correct level of hardness. You can also use rainwater collected from a safe source.

To adjust the ph of your water you can either use a muslin bag containing peat moss to acidify your water or you can use calcium carbonate sand to alkalinify it instead. In order to reach the correct ph level.

All these procedures are complicated and time consuming and even prone to error. Messing with your tap water usually means you will have to monitor changes in your water conditions to maintain it. To make this complicated process a little easier it is best to prepare large batches of water in say a 200 litre barrel all in one go and then draw off water as needed.

I recommend that you don’t bother with all this messing around and just buy fish that can do well in the water that comes from your tap. There is usually quite a variety of fish that will suit your water conditions but you may have to avoid a particular species of fish that you might be keen on.

What water conditions are best for fish?

Normally the ph used in most freshwater aquaria ranges between 6.0ph and 8.3 ph. However Lake Tanganyika fish like an even higher ph, even as high as 9.0ph. And they also like hard water. Ph nearly always varies together with hardness. High ph above 8.0 usually means very hard water, while low ph of 6.4 or less coincides with soft water. Some amazonian fish like water that is of a ph less than 6ph and have very soft water.

Most of the commonly available fish in your aquarium prefer an average ph around 7ph and a medium level of water hardness. Not only that but such species can also tolerate a wider variation away from this medium than other more exotic species. Tank bred fish that have been bred in aquaria for several generations are overall more adaptable to variations in aquarium conditions compared to their wild caught counterparts.

Most average species will live in a wide range of possible water condititions. However, when it comes to breeding the ph and hardness must more closely resemble the fish’s conditions in the wild. Only then will some fish be capable of breeding and their eggs hatching.
Water hardness

This is a measure of the amount of dissolved minerals in your fish’s water. The most common minerals are calcium, magnesium and sodium.

These dissolved minerals are also essential for the health of your fish and plants.
Most cyprinids, tetras, rasboras and similar river fish like soft water. Most livebearers, Malawi fish and Tangayikan fish prefer quite hard water.

Plants also show a similar type of preference for different levels of hardness depending on the plant species.

Iron for fish health

Plants require minute levels of dissolved iron for optimum health as do fish. Fish acquite iron from their diet while plants will absorb it directly from the water. Pure iron quickly rusts in water making it unusable for the plants and animals. Feeding fish iron rich fish food will not only provide iron for the fish but allow the fish to provide manure that is rich in iron for the plants use.

Dissolved oxygen in water that fish breathe

Dissolved oxygen is essential for fish to breathe. The main source of oxygen in an aquarium is through the surface of the water. So a large surface area of water is essential to allow sufficient oxygen to dissolve into the water to replace the amount of oxygen that the fish breathe in through their gills. Also excess carbon dioxide that the fish release into the water from their gills has to be released from the water through the surface of the water. Plants also give off oxygen when they are in bright light, but will release a small quantity of carbon dioxide at night.

It is best not to rely on the quantity of oxygen that plants produce during the day to supplement the amount from the surface because this source of oxygen stops at night. If you see your fish gasping for air very early morning this is a sign that there is not enough oxygen and too much carbon dioxide in the water in the night so you will have to reduce the number of fish in the aquarium. This can also be a sign you have too many plants.

Fish waste in water

One lethal cause of fish deaths is ammonia poisoning which burns the skin and gills of the fish while also displacing oxygen in the water. Ammonia comes from fish waste and from decaying fish food and other decaying organic matter. In a new aquarium there will be no ammonia but this will build up over the fish few weeks. If you are new to fish keeping you will see your fish as being fine for the first week and may not realised that the fish are slowly but surely poisoning themselves in their own waste matter.

To overcome this you need some way to remove the ammonia as it gets created. You will have to for the first 6 weeks have to do daily water changes, use a filter and make sure that you under stock your tank until it is mature. Also avoid any uneaten fish food being left in the tank that will quickly rot and cause an ammonia spike.

A filter is not just for removing particles from the water but also for providing a base for the growth of bacteria that digest ammonia converting it into nitrite which is also poisonous. Later on another set of bacteria develops that will digest the nitrite converting it into nitrate which is much less harmful. This process takes between 4-6 weeks from new. So partial water changes are needed daily until the filter matures.

This is better explained in cycling your aquarium

Plants take up nitrate but usually not enough so you will need to keep doing partial water changes, perhaps once a week. 10% of the water changed is a reasonable amount of water change.

During this filter maturation period you should test your water daily with a test kit and if the ammonia or nitrite reading becomes particularly high then you will have to do another partial water change to bring it down to acceptable levels.

Why do my fish keep dying?

two dead goldfish neglected in an aquarium

Why do my fish keep dying?

Your fish die because of:
(1)Over feeding.
(2)Chlorine in tap water.
(3)Build up of fish urine and poop over time.
(4)Buying too many fish.
(5)Buying sick fish.
(6)Some fish attack other fish.

Mistakes beginner fishkeepers make

two dead goldfish neglected in an aquarium
two dead goldfish neglected in an aquarium

There can be several reasons for the death of your fish; however for beginners the main reason is new tank syndrome. This is a situation where you have bought new fish and placed them in a newly set up aquarium. Your fish start dying and you are unable to explain the cause. This syndrome is usually experienced by new fish owners who have yet to master keeping fish safe, healthy and alive. Here are some things that you should look out for and avoid to explain and prevent new tank deaths

  • Uncycled aquarium & filter
  • Water chemistry problems
  • Diseases
  • Poor diet and overfeeding
  • Over population
  • Wrong type of fish
  • Buying sick fish

Uncycled aquarium & filter

dead catfish on the tank floor
dead catfish on the tank floor

Most fish owners will be buying their new pets along with new equipment, such as an aquarium and a filter. They will fill the aquarium with water and then put in the fish and they will think that the work is done. This is a common error by most new fish owners. What do you do about fish poop and urine? Aquariums don’t come with toilets. So you need to provide one. You have to provide a biological toilet. This comes in the form of a filter with a sponge or gravel. Even before you introduce your fish, you need to set this up. You need to give the bacteria in the filter time to build up and be capable of removing fish waste. This bacteria neutralises fish poop and urine, breaking it down into nitrate.

Remember, you can’t just syphon/pump out the fish poop from the aquarium. The ammonia from the fish waste is still in the water.

Take note that the same way human bodies have good bacteria that can protect them from harm, so does the aquarium. An aquarium and especially the filter must have good bacteria that can protect them from risks to their health. The bacteria work by neutralizing or converting toxins that are produced by the fish’s droppings and urine such as ammonia and nitrites.

Without good bacteria, these toxins build up in the aquarium. When they reach dangerous levels, the fish will absorb these toxins and cause them to become ill. Since it is often difficult to detect if a fish is sick, new fish owners will only discover it when it is too late and the fish are dead or about to die.

It takes time for the healthy bacteria in the filter to build up, between 4-6 weeks before a healthy population of bacteria develops in the filter capable of fully removing fish waste products. So, what do you do in the mean time? You have to do daily partial water changes to dilute these toxins. Perhaps, remove 5% of the water and top up with (chlorine free) fresh water.

dead fish on the tank floor that needs removing asap
dead fish on the tank floor that needs removing asap

This explains a common pattern to newly bought fish that will be fine for up to a week or longer. Then something seems to change and the fish start getting ill. Finally they start to die. And, the few fish that survive start to get better and if all is well the survivors live a long time.

This is all explained by the cycling of the filter and the fish waste product. When the fish first enter a new aquarium with fresh water there is no waste matter in the water. As the fish start to poop and urinate in the water this waste starts to build up. This poisons the fish. Slowly the bacteria in the filter build up and digest this waste cleaning the water, but this takes weeks to establish.

Water chemistry problems

Fish require a delicate balance in the chemicals in the water. Clear water does not necessarily mean an ideal environment for the fish. Ammonia, nitrites and nitrates are some of the chemicals, which when uncontrolled, can cause significant harm to your fish that will eventually lead to death. These toxins are from the waste your fish produce. These are harmful toxins that should be neutralized or kept at a minimum during the course of your taking care of the fish.

Cycling explained in full here

When looking after fish as pets you are not necessarily taking care of the actual fish themselves but rather of the water quality instead. Measuring devices and kits are available to keep a check on the various chemical parameters of the water of your fish tank. You must also have keen observation, noting changes such as the tinge of the water, any discoloration of the gravel in the aquarium or the behaviour of your fish. However, as a beginner, if you rely solely on observation, the toxic levels will already be too high to before you understand that something is wrong. At this point any chance for survival of your fish is slim.

Tap water usually contains chlorine which is lethal to your fish. To remove it leave the water standing for 1-2 days before adding to your aquarium. Alternatively, use dechlorinating medication that removes chlorine immediately from tap water.
Check the ph and hardness. Ph between 6.6 – 7.6 is okay for most fish. Test the hardness level. A moderate level of hardness is ideal for most beginner fish.


Don’t buy sick fish! Beginners often buy fish that have illnesses from the pet shop. This is easier said than done. Check the pet shop aquarium if there are any sick or dead fish in there. Check if there are any spots on the fish or markings or fungus like patches. Make sure the fish are active and swim towards food. Don’t buy fish that are sulking or have clamped fins (ie fins held close to the body). Check the fish has bright colouration.

Another cause for fish death is because of disease. As the water quality becomes poorer from elevated levels of toxins, the fish health also becomes poorer with it. When the fish become weaker, they are more vulnerable to disease. A healthy fish will normally be able to resist these illnesses but a weakened fish will succumb to them.

Some examples of these diseases are bacterial infections, fungal infections, internal parasites in the fish’s body, dropsy and other opportunistic diseases. Most new fish owners will attempt to cure these diseases by adding antibiotics, anti-parasitic or anti-bacterial medicine into the water. However, without treating the underlying cause of the disease, which is the toxicity from waste matter, there will still be fatalities, despite the medication. Experienced fish owners are able to nurse a fish back to health where a beginner may or may not succeed.

Another factor is not quarantining new fish from your other fish. This allows the new fish to spread any illness or parasite it may have to the other fish. It is also a good idea to medicate new fish with antibacterial and anti parasitic medicines.

What even some experienced fish keepers fail to do is quarantine new plants. They too should be medicated. Plants can be medicated with larger doses.

Poor diet and overfeeding

Most new owners will enjoy feeding their fish. Who wouldn’t enjoy seeing their fish swim towards the food and follow the trail wherever you sprinkle the food? It is also fun to see some fish diving towards a food pellet that sinks towards the bottom of the aquarium. Ironically, feeding your fish or rather overfeeding is also one of the main causes of fish death.

Fish should be fed once a or twice day, with the fish eating everything within 5 minutes and always remove uneaten food. But most new owners will feed their fish every chance they get. On top of this over feeding, other members of the family may also be feeding the fish on their own without the owner’s knowledge. Fish food that is uneaten, such as food left floating on the surface of the water or sitting on the aquarium bed will rot and pollute your aquarium, leading to the same problems as fish waste. Rotting food in the aquarium is the second biggest cause of fish deaths after new tank syndrome.

Over population

Too many fish in a tank means that the fish can’t get enough of the oxygen in the water. So they drown. The first sign of this is the fish gasping for air at the surface of the aquarium. There isn’t a strict rule on the ideal number of fish for a certain size of aquarium. More experienced fish owners recommend a ratio of 1 inch of fish for every 1 gallon of water. Take note that the 1 inch is meant to be measured on each fish’s eventual adult size. The more fish there are, the greater the chance for oxygen deficiency, self pollution and diseases to spread.

Another cause of death for fish is the population itself. Despite the care you make on making a balance in the water chemistry, proper feeding schedule and best equipment you can provide, your fish may still die because there are just too many fish in too small an aquarium. But problems may also arise if you have the wrong combination of fish species.

The wrong combination of fish can also lead to stress and deaths. If you put together an aggressive fish with a more passive or smaller fish, the passive fish may be bullied. In their natural environment, a passive fish would be able to escape the aggressive fish, but in an aquarium they have no chance for escape. The constant stress will cause death.

Wrong type of fish

Finally, the beginner may have bought a difficult to care for species of fish. Difficult fish may need special water requirements, special dietary needs or some other type of specialised care. You must always ask the pet shop owner if the fish you are buying are beginner community fish to avoid such problems. Only buy more difficult fish when you have more experience.

You should buy popular starter fish such as gold fish, tetras, platies, swordtails and bettas. These are colorful, active and most importantly easy to care for. Avoid buying difficult fish such as saltwater fish.

Recommended compatible fish groups here


Once you have mastered the two main causes of fish death which is new tank syndrome and rotting uneaten food in the aquarium you will have a good chance of keeping your fish alive long term. And, if you follow all the above advice you should hardly ever see a fish death in your tanks. If you follow all this advice, not only will your fish stop dying but you will see your fish in full glowing health.

Clean and clear aquarium water

Clean and clear aquarium water should be all aquarists goal

Clean and clear aquarium water: A guide to water quality and management

Also see: Cure and prevent cloudy or green water

and Why does my aquarium get dirty

Clean and clear aquarium water should be all aquarists goal
Clean and clear aquarium water should be all aquarists goal

Water may appear clean and clear but, actually, be absolutely toxic to your fish. You need to be able to create water that is clean and healthy for your fish. Below I will explain how to create clean and clear water and how to maintain this indefinitely by establishing a balanced ecosystem. It can be said that you are not taking care of your fish but rather you are taking care of the water the fish live eat and breathe in.
A fully-functioning aquarium is a balanced ecosystem that needs to remain balanced in order to let your fish thrive. Setting up and maintaining this ecosytem is the first and most important step towards taking good care of your fish.

Water composition

In order to understand how to successfully manage your aquarium water, you need to become familiar with the various attributes of water that aquarists generally deal with. The water in your tank will have more in it than simple H20, and frequent testing is the best way to keep all of those additional elements in check. Some of the attributes and chemicals worth paying attention to follow:

  • Temperature – your water needs to have a controlled temperature for your fish to survive. Tropical aquariums are typically heated to a temperature between 23–28° C (74–82° F).
  • pH level – This is the measure of your waters acidity, and is affected by its hardness. Certain fish have pH requirements determined by their natural habitat, but a range somewhere between 6.5–8.2 is the norm.
  • Hardness – The amount of dissolved minerals in your water contribute to its hardness. Soft water generally carries a lower pH level. Most fish are tolerant of moderate hardness between 100–250 mg/l.
  • Chlorine and chloramine – These chemicals are added to municipal reservoirs to keep your tap water clean and safe to drink. They are toxic to fish, however, so you will need to remove them from your water. Chlorine will evaporate on its own if left to sit for a few days, but chloramine requires the use of a water conditioning product to successfully remove.
  • Phosphate and other minerals – These are substances that are usually ignored by most aquarists. But there are times when it is necessary to test for other substances. Such as when algae becomes a persistent problem or plants are not growing.
  • Ammonia – Ammonia is toxic to fish and is caused by decomposing waste, and the point of your aquarium filtration system is to remove harmful ammonia by converting it into nitrite and then nitrate. That takes place during the nitrogen cycle, which will be covered in more detail below. The optimal level of ammonia in your water is zero. Anything above .25 mg/l of ammonia means you need to perform a water change.
  • Nitrite – A secondary element of the nitrogen cycle, nitrite is not as toxic as ammonia, but it reduces the ability of your fish to oxygenate their bloodstream. A normal tank should not have more than .5 mg/l of nitrite. If it does, it is time for a water change.
  • Nitrate – The end product of the nitrogen cycle’s chemical conversion. Not as harmful as nitrite or ammonia but still harmful in high doses. Nitrate can be tolerated at levels up to 40 mg/l.

Cycling your aquarium water

See cycling for more info

Since substances like ammonia and nitrite are toxic for your fish, you need to remove them from your water on a continually. Fortunately, once matured, your filter will automatically remove them for you. Your aquarium’s filtration system is designed to host a range of beneficial bacteria that convert ammonia into nitrite, and nitrite into nitrate; a process called the nitrogen cycle. In order for that to happen, however, you need to set up your aquarium for cycling.

Since fish produce ammonia, they are typically used as the beginning point of the nitrogen cycle. After being added to a tank, very frequent water changes are needed to keep the fish healthy until the bacterial colony which feeds off the ammonia has developed sufficiently. Fishless tank cycling can be achieved using pure ammonia, as well.

Once ammonia is in the tank, bacteria will naturally show up to begin consuming it and converting it into nitrite. This can be speeded up by introducing a working filter from another aquarium, since a colony of bacteria should already be present established there. If this is not an option, then they will develop, on a new filter, slowly over 30-60 days. A secondary layer of bacteria will also appear that will convert the newly created nitrite into nitrate.

The end result of growing these bacterial colonies in your aquarium filter is that your water will essentially be recycling its own waste. However, nitrate still needs to be reduced through partial water changes. Luckily, that is only a weekly task. If you are keeping fish in your tank while cycling, you will need to perform large daily water changes until the ammonia levels fall to near zero.

Setting up a water management routine

Once your tank is properly cycled, you will still need to monitor your tank’s water. Since the nitrogen cycle is taking care of your immediate concerns over waste matter recycling, you can keep your water quality high with minimal effort. The only daily task that is necessary at this point is checking the water temperature.

Weekly tasks include performing a small water change, between 10–25%, as needed according to the nitrate level of the tank. You should also be testing your water every week in order to gauge the nitrate level as well as detect and prevent any possible ammonia, nitrite, or pH problems that may spring up, before they get serious.

Your monthly tasks should include a vacuuming of the tank gravel, a squeezing out of the excess dirt from your filter sponge and a scrubbing to remove any algae present in the tank. Never use tap water on your filter sponge. Squeeze out the sponge using some water from the aquarium. This avoids harming the beneficial bacterial colony growing on it.

Common water quality problems

One of the most evident signs that your aquarium water has a problem is if the smell changes. Aquariums generally have a pleasant lakeside scent to them once they are properly cycled, but excess ammonia and other elements can change that, giving you a warning to test the water and change it quickly.

Most often, bad-smelling water is a sign that there is too much waste in the tank as a result of overfeeding. Your fish should generally eat all of their food in two minutes or less and not leave any to rot. Excess food will rot which releases excess ammonia that will poison your fish. Occasionally your fish will go off their food. Feeding at this time will just result in food being left uneaten and rotting. Remove any uneaten food using a siphon.

A fish that dies in the tank should be removed immediately. A rotting fish will release a lot of ammonia which your filter will not be able to cope with.

Algae is another common result of poor-quality aquarium water. Again, excess nutrients (especially nitrate and phosphate) can allow algae to bloom, turning your water green and presenting problems for your fish. If you are not overfeeding your fish, then algae may bloom because of an excess of yellow light. Also, be sure to keep your aquarium out of direct sunlight.

If you pay attention to your water and follow the guidelines mentioned above, you should have a tank full of clean and clear aquarium water for your fish to enjoy.