Removing phosphates from the Aquarium

Definition, what is phosphate

Phosphates, seen as PO₄ in the scientific tables, are all around us. They are a compound that is present inside all living things as they are one of the building blocks of cells and they are nearly always present in any water that is used by us or is present in lakes and rivers. PO₄ is basically a phosphorous atom that has four oxygen atoms attached to it and this is often the dissolved compound that inhabits the water, there are other forms of phosphates that use a different build of atoms but these are usually insignificant and most of the aquarium testing kits will only test for PO₄.

If this is allowed to build up in the aquarium water it can be a food supply to algae which can quickly spread, algae in itself does not harm fish but the colonies of algae can lower the oxygen levels in the water meaning less available oxygen for the fish or invertebrates that we keep. To keep phosphates in check we need to know where they are coming from so that we can reduce the intake into the aquarium and we also need to know how to remove them once they have actually entered the aquarium.

Sources of Phosphates in the Aquarium

There are very many ways that phosphates can enter our aquarium water and here is a basic guide to the main culprits.

Uneaten food can break down over a period of time and phosphates will form as the phosphorous in the food combines with oxygen, only feed the fish enough food that they can eat in 5 minutes, no food should be left lying around at the bottom of the aquarium.

Plant decay is another large source of phosphates, rotting leaves will contain phosphorous so if you see any leaves detach from the plants or start to lose their colour and go brown, they need to be removed straight away.

Fish waste will also produce phosphates if left to break down in the substrate, using a gravel vacuum on a regular basis will remove nearly all of the fish waste but only do a percentage of the substrate each time or you could remove a lot of beneficial bacteria in one session.

Like rotting food and plants any dead fish in the aquarium will break down over time releasing phosphates into the water, when you do your daily temperature check, do a head count of your fish and if any are missing locate the body and remove it from the aquarium.

Mains water will probably contain phosphates, this is a natural occurrence. Treating your water before adding it to the aquarium should keep these under control.

Artificial pH adjusters and water buffers definitely contain phosphates, there are other ways of buffering your water or adjusting the pH without having to resort to using these products, adding these to the tank can cause more problems than they are worth.

Aquarium salts added to the aquarium will also add phosphates, take the time to read the labels on the packaging and you will see the phosphate content, adding salts can be fine for a short term solution to some diseases but these should not be used on a regular basis.

There are testing kits available for checking the level of phosphates in your aquarium water but these can only test for inorganic phosphates (PO₄), the organic phosphates are trapped in the aquarium but these are fine in this state, there are several companies that produce the testing kits so have a browse around and find the best one for you, on a personal basis I have always used API brand testing kits which use the liquid testing method, I have always found the testing strips to be less accurate as they test for several things at once in a broad spectrum. The liquid testing kits will test for one thing at a time and give you a better idea of what is going on in your aquarium.

Removing Phosphates from the Aquarium

The easiest method of reducing phosphates in the aquarium is by performing water changes, all of the phosphates will never be removed but water changes will keep them at a reasonable level just as they do with the nitrate levels.

Tank maintenance if performed properly will also keep the phosphate levels down, every now and again remove some of the décor and scrub it clean, gravel vacuum areas of the substrate as phosphates will be lurking in there. Never gravel vacuum all of the substrate in one session as it will remove most of the beneficial bacteria as well, do a different area of the substrate on a rotational basis.

Filters can get clogged over a period of time so every now and again rinse out the sponges with old tank water, never use mains water for this, the sponges will often have debris on them which rots away releasing phosphates.

One quick method for removing most of the phosphates is to add some carbon to the filters, this will soak up the phosphates over a time as well as any other dissolved impurities. Always remember when the carbon was added as it will become saturated after about a month and start to release the impurities back into the aquarium water, make sure that you replace the carbon before this is allowed to happen.