The best method is to use two containers: one for disinfecting, the other for rinsing.

The best active ingredient to use in the disinfecting container is formaldehyde, which is available from fish and aquarium shops, and online.

The normal concentration of shop bought aquarium formaldehyde is 37%.  Adding 2 tablespoons of this to a medium-sized bucket will be enough to kill bacteria and parasites.

Simply dip the net, scraper or whatever into the formaldehyde solution, then into the rinsing container which contains nothing but clean water.  There is no harm in storing the equipment in the disinfecting container either.

A good tip is to add a small amount of dye to the disinfecting container.  Not only will this easily distinguish the otherwise colourless disinfectant from the rinsing water, it will also give an indication as to when the rinsing water needs changed as it gradually gets the colour of the dye.

The problem is that the water inside the ornament does not circulate.  This means it is low in oxygen and high in bacteria.  In other words it is stagnant, and the ornament has become a disease factory.

Bacteria escape and enter the main body of water, making fish sick and killing them.  Without knowing what is causing the problem, an otherwise diligent fishkeeper can end up very frustrated trying to find out the cause of the infections.

Thankfully there is an easy solution that doesn’t mean removing every hollow ornament.  The silicone sealant that is used to hold aquarium glass together can be injected into the eye sockets of a fake skull, the opening of a sea shell, the windows and doors on model houses, and so on.

This means that the ornaments are no longer hollow (even though they look it), and interesting or themed aquariums don’t need to lose their character to be safe for fish.

There are a number of practical steps that can be taken to control pond algae, most of which form part of basic pond management anyway.

Pond Construction

By following the steps outlined in the earlier blog post Build the Perfect Goldfish Pond, pond algae will already be less of a problem.  By making sure the pond is not positioned where a lot of debris will fall into it, there will be less nutrients for the algae to use for growth.  Using a black liner to absorb sunlight rather than reflect it into the water also deprives algae of the conditions it likes.  If the pond has sloping sides leading down to a bottom level, it makes the job of collecting any debris that does fall in easier, as it will be more localized.  Finally, have a pond that is deep enough to prevent strong sunlight penetration, and large enough to reach its own level of ecological balance will also work as an excellent preventative measure.

Plants

Plants can be used to provide shade over the water where long periods of direct sunlight are a problem.  Water lilies are the obvious example, but there are many different types of aquatic plant that can be used.  Plants also have the added effect of using up the nutrients that algae would otherwise thrive on.

Cleaning

It is a fairly obvious point, but floating plant debris should be removed from the surface of the pond as often as it appears.  If it remains long enough to sink to the bottom it starts to produce the nutrients that fertilize the algae, and is more hassle to remove.

Isolation

If fertilizers are used on surrounding lawns, it is vitally important to prevent run-off from the lawn into the pond.  If the pond is at a lower level than any part of the lawn, some sort of barrier needs to be  in place that will direct contaminated water around the pond.  Garden fertilizers are designed to make green things grow very quickly.  They can cause disastrous algal blooms in goldfish ponds.

Barley Straw

When barley straw is placed in water it starts to decompose.  Chemicals released during the decomposition process are effective in stopping algal growth.  Bunch it inside a net – a couple of large handfuls should do for an average sized pond – and when it turns black its job is done.  Repeat the process as necessary to help control algae.  Barley straw extract is also available as a commercial product.

Skimmer

A skimmer is a mechanical device, powered by electricity or battery that removes floating debris from the surface of a pond.  There is no need for one unless manual surface cleaning doesn’t take place.

UV Filtration

Ultraviolet lamps can be purchased which are then placed in the pond water.  As the algae suspended in the water pass over the lamp they are exposed to UV rays.  These rays destroy algal DNA, and the result is usually a very clear pond.

Chemical Treatment

Anti-algal chemical treatments are available and offer a quick and easy solution.  Although generally not harmful to goldfish, they can be poisonous to frogs, snails and insects that help create an ecological balance and increase biodiversity in the pond.  As well as that, they are not always effective against all (over 17,000) types of algae.

However, that is in a natural setting.  When a heron visits a goldfish pond, it doesn’t need any patience.  There is crystal clear water with brightly coloured goldfish that can be picked off at will.  No need to wait for a fish that is the same colour as the murky water it is swimming in.

Apart from the obvious problem of quickly removing goldfish from a pond, herons cause a number of other problems for goldfish.   Firstly, they are disease carriers.  Secondly, if they don’t introduce a disease to the pond, an attack could increase stress levels in the remaining goldfish to levels that make them susceptible to disease.  Thirdly, they can spear a goldfish only to discover it is too big to swallow.  When that happens, they leave the goldfish by the side of the pool to die.  Whether or not suffocation kills it before the stab wound, it will die in agony.

Therefore it is very important to do everything possible to prevent heron attacks, and there are a number of methods available.

Hiding Places

Put some sections of pipe or upturned flower pots with entrance holes in the pond.  Goldfish can use these to shelter in when they see a heron at the surface of the water.  Unfortunately the goldfish will need to have been attacked at least once before knowing what a heron looks like, and taking advantage of the hiding places.

Netting

Netting stretched tightly over the surface of the pond will prevent herons taking goldfish.  The problem with this method is that it is unsightly and makes feeding the goldfish more awkward than it should be.  Having said that, a net should be used for a while after the first heron attack.  This is because the heron will be sure to return for more easy pickings.

Fishing Line

Herons usually won’t land in the pond, because they know it will scare the goldfish.  They prefer to walk up to the pond and launch a surprise attack.  A length of fishing line across the path of the heron about a foot (30cm) away from the pond and a foot off the ground will give a heron a fright when it trips over it.  The RSPB recommend using two lengths at about 6 and 12 inches off the ground.  However, herons will get wise to this trick, and use other approaches.  Then the whole pond will have to have a perimeter round it.  Eventually the heron will learn to land inside the perimeter, or on sturdy plants inside the pond.  If the pond is quite large, they will most likely land in the water anyway.

Scarers

Various forms of scarers can be used.  Some rely on a constant flow of water causing sudden movement on a hinge, others use trip-wires or infrared detectors to set off loud bangs or squirt jets of water.  Whatever method a scarer uses it will most likely be expensive, and a patient heron will eventually get used to it.

Plastic Herons

Plastic herons are sometimes placed in ponds to make real herons think the territory has already been claimed.  Many goldfish pond keepers dispute this, and point to the fact that herons looking for a mate will very often land beside a plastic heron, realize it’s not real, then eat all the goldfish.  On top of that, a hungry heron won’t care if another heron appears to stand between it and a meal.

Routines

Probably the most effective long term method of preventing herons taking goldfish is to train the goldfish when to come to the surface of the pond.  Always feed them at the same time every day, so that they eventually get to know when to come up.

On the other hand, break up the routine of going to the pond.  Herons watch and wait before deciding when to attack a goldfish pond, and will not do it when they think a human will be in attendance.  They will work out when the coast is clear and fly in.

Approaching the pond at unpredictable times but feeding at predictable times means that the goldfish will know not to surface every time they see a figure at the side of the pond.

Obviously if a house is left unattended at regular times for long periods this method will not work.  Neither will it work at the crack of dawn when most people are still in bed.  However, if it is done when possible it is very effective.  It foils the heron’s plan at the earliest stage – before it gets anywhere near a pond.  Outwitting the heron is something no fishing line, net or banger will ever be capable of.

Summary

It’s a game of cat and mouse.  Herons will always be attracted to goldfish in a pond.  Hiding places should be provided as a matter of course, and trip-wire may be necessary at some point.  However, the main thrust of any anti-heron activity should be to make the pond more hassle for the heron than it is worth at another pond.  Herons will visit a number of ponds looking for an easy meal, so a pond that gives them a bit of hassle should quickly get taken off the list.

However, other herons will take a look, so it’s important to remain vigilant and keep on top of the situation.

With so many different types of filter available – each with very persuasive marketing all over the packaging – it is hard to know which is the right one for any given goldfish tank.

How Filtration Works

Mechanical filtration – this is simply the process of making water pass through a substance that will stop particles of dirt, faeces, uneaten food and other solid matter that are carried in the water. Examples of mechanical filtration include mesh, netting, sponge and filter wool.

Biological filtration – this is the process of turning poisonous ammonia (a by-product of decaying plants, food and goldfish faeces) into less harmful nitrates. These nitrates are then removed by regular water changes. Biological filtration is performed by bacteria that colonize the large surface area provided by sponges, gravel and filter wool. These bacteria can also be present in specific plant roots. Sometimes the mechanical filter and the biological filter are contained in the same physical item – e.g. a sponge – and sometimes they are two separate entities i.e. the water passes through a mechanical filter, then a biological one. Biological filters should only be cleaned in tank water, never in running tap water.

Chemical filtration – this form of filtration is used to remove chemicals from the water that are dissolved rather than suspended in the water, and that cannot be broken down by bacteria normally found in goldfish water. The most popular form of chemical filtration is activated carbon, that removes a number of toxic chemicals from the water, and is often used after adding medicinal chemicals to water. Another example is ammonia remover. Although biological filtration usually deals with ammonia, sudden increases in ammonia can overwhelm a biological filter.

Types of Filter

There are several different types of filter available, each with its own advantages and disadvantages. The following list summarizes the most common types.

Box filter – a very cheap, small plastic box that sits in the back corner of an aquarium, and is filled with filter wool and/or activated carbon. This type of filter is only suitable for very small tanks with very few goldfish in them, or in spawning tanks. It can also be used in larger tanks for quick and easy chemical filtration if it is filled with activated carbon.

Under gravel filter – a tray the same size as the bottom of the goldfish tank with one or two upright tubes attached to the back corners. It needs to be covered with gravel, because it is the gravel that acts as a mechanical filter, and provides the surface area for the ammonia-nitrite-nitrate bacteria to colonize. An under gravel filter is also cheap, but it is not very efficient and causes problems for aquarium plants.

Internal power filter – a two part filter consisting of a pump and a chamber containing a sponge. The sponge acts as both mechanical and biological filter. It provides good circulation and oxygenation of the water, and the sponge makes a very happy home for biological filter bacteria. However, the surface area is relatively small, so it can’t be used in large tanks. Also the filter itself may be a bit unsightly in the tank.

External power filter – works the same way as an internal power filter but sits outside the goldfish tank, often hanging from the top edge of the back of the tank. It is a popular choice for small aquarium owners as it gives the inside of the tank a more natural look, but it has the same limitations as an internal power filter.

Canister filter – this is a large external canister that works well in large aquariums. Most canister filters come with mechanical, biological and chemical filtration as standard. They work extremely well and hold a lot of filter medium, so don’t need cleaned very often. They are however for the more serious goldfish enthusiast, and this is reflected in the price. Also, they are not small and need room. This will often mean a custom-built cabinet to hide the canister.

Diatom filter – used for one off cleaning of the water, a diatom filter is a mechanical filter with a microscopically fine filter medium that can filter out almost all physical impurities in the water, right down to micro-organisms. A diatom filter cannot be used continuously, the medium clogs up too quickly. It is used at regular intervals to keep the water crystal clear.

Wet/dry filter – more likely to be found in large saltwater aquariums than goldfish aquariums, wet/dry filters work like sewage treatment beds. Water is trickled or sprayed onto a mechanical filter medium which provides high levels of oxygenation. It then passes on to the biological filter, and possibly a chemical filter. This type of filter is the most expensive and requires the installation of plumbing.

Summary

For most goldfish owners an internal power filter or an external power filter will do very well, with a box filter on hand for chemical filtering when needed. However, it is important to choose filters that will put enough water through to actually keep the water clean. At least 4 times the volume of the aquarium per hour, and more if the tank is heavily stocked.

Also, test the aquarium water regularly to make sure ammonia and nitrite levels are not rising. If they are, it could be a sign that biological filtering is not coping. If the water is cloudy or dirty, then the mechanical filter needs upgraded.

There are 4 main aspects of water quality to test, all related to each other chemically.

Ammonia and Nitrite

Ammonia and nitrite levels can build up to dangerous or even fatal levels in a new tank. Ammonia is present in goldfish faeces, and is produced by rotting plant material and uneaten food. Certain types of bacteria feed on ammonia, turning it into nitrite, then nitrates. Until these bacteria are present in sufficient numbers, the ammonia and nitrite levels will rise.

The ideal levels of ammonia and nitrite are zero, but small amounts (less than 4 parts per million) can be tolerable. However, in a new tank with no ammonia-feeding bacteria the ammonia level will peak after a week, with the nitrite levels peaking a fortnight later. It is very important to have chemicals to deal with these toxins at hand during the first month of the aquarium.

Nitrate

As mentioned earlier, nitrites are eventually converted to nitrates, which are much less toxic to goldfish. Nitrates are still dangerous, and although goldfish that have been in the aquarium for a long time can build up tolerance, new goldfish will struggle to survive in water with high nitrate levels.

Regular, adequate water changes should be enough to prevent nitrates building up to dangerous levels. If testing shows high nitrate levels, either increase the frequency or the volume of water changes.

pH Level

pH is a measure of acidity and alkalinity. The scale runs from 0 (most acidic) to 14 (most alkaline) with 7 being neutral.

The optimum pH for goldfish water is slightly alkaline, but goldfish are happy with anything between 6 and 8. The most important thing to remember about pH management is that changes in pH are more harmful to goldfish that being outside the optimum range. Stable pH is the key.

Water Hardness

Water hardness is important because it regulates the pH of the water by a process known in chemistry as buffering. In practice it means substances dissolved in the aquarium water absorb the impact of changes that would otherwise change the pH of the water.

There are two measures of water hardness: general/total hardness and carbonate hardness. It is only necessary to measure one or the other, not both.

General/total hardness is often expressed as dH, GH or dGH. It should be at least 4dH to ensure buffering works, and goldfish can tolerate levels up to 20dH.

Carbonate hardness is expressed as mg/L and should be between 70mg/L and 400mg/L.

Testing Routine

Testing for ammonia and nitrites should – in theory – be unnecessary in an established goldfish aquarium. Testing for nitrates should be done with every water change, i.e. weekly. The same goes for pH and hardness tests.

The other time to perform testing is when something appears to be wrong: goldfish not eating, one dying, new fish dying and upon discovery of illness or disease.

It is also very important to record the results of testing. If there is an outbreak of chilodonella for example – which can be caused by poor water quality – it is no good knowing what the pH of the aquarium water is on the day of the outbreak if you can’t remember what it was in the days and weeks running up to the outbreak.

1. Change the goldfish diet to one with less protein and more carbohydrates. This will build up fat reserves in the goldfish, which will give them energy over Winter. If the water temperature drops below 10 Celsius, stop feeding them altogether.
2. Clean the pond. Remove all the organic material from the bottom of the pond (dead plant material and goldfish droppings). If possible remove the goldfish from the pond, drain all the water, clean the bottom of the pond, and replace the goldfish in clean water.
3. Cut away dead or dying leaves on plants. Some plants will require more severe pruning, so get appropriate advice from a good aquatic or garden centre.
4. If a biological filter is used, put new filter medium into it to maintain water quality all through the Winter.
5. If the goldfish pond is likely to have autumnal leaves falling into it, pin a fine mesh over the surface of the water to catch them. If they get into the water they will fall to the bottom and the decomposition will remove oxygen from the water, and thereby from the goldfish.
6. Put a hiding place for the goldfish in the pond. Winter is tough on the animals that eat goldfish too, and they will take an easy meal if they see one. An upside-down flowerpot or overhang arrangement will work.
7. If ice forms on the surface of the water, melt a hole in it. This allows oxygen to enter the pond, and carbon dioxide (and other toxic gases) to escape.

Aquarium plants have the same needs as any other plant: somewhere to put their roots, nutrients for sustinence and growth, and carbon dioxide and light for photosynthesis.

Substrate

Substrate is the commonly used name for the sand that aquarium plants take root in. It needs to be coarse enough for water to circulate, and fine enough for the roots to take hold in. The optimum size is between 1mm and 3mm, and the optimum depth is between 5cm and 10cm.

Pea gravel and glass are no good for maintaining aquarium plants. There are commercially available substrates that are designed to promote healthy bacterial growth within it, and to provide trace elements that would be provided by water flow in a natural setting. The other advantage of commercial substrate is that is looks a lot nicer than sand or gravel.

Of course, there is nothing wrong with putting pea gravel or glass over a good substrate that might not look as nice.

Nutrients

Some plants will get all the nutrients they need from the substrate, but others will require feeding. As well as trace elements, plants also need nitrogen, phosphate and potassium. A good portion of this will come from goldfish faeces, but the amount of fish in the tank plus the cleaning regime will have an impact on how much of these compounds are in the water.

Again, commercial aquarium plant food is available and is often necessary to maintain healthy aquarium plants.

Carbon Dioxide

Plants need carbon dioxide to make sugar, which they turn into energy for growth, repair and reproduction.

There are various methods for introducing extra carbon dioxide into the water, ranging from the home-made to the professionally expensive.

It may seem counter-intuitive to dissolve carbon dioxide in the water that goldfish need to get oxygen from, but the two gasses are dissolved independently, and the amount of one does not effect the other.

Light

It’s best to use flourescent light, as standard incandescent lights will heat the water and use far more electricity. For healthy plants, simply mimic natural summer time light. Leave it on for about 14 hours a day for the aquarium plants to get all they light they need.

Maintanence

Once the aquarium has been prepared for plants, the maintanence is fairly straighforward. Remove floating plants, dead or unhealthy looking leaves, and keep an eye on the goldfish for signs of disease.

It is usually only necessary to change between 20 and 30 percent of the water volume, but this depends on how many goldfish are in the tank and how often they are fed. If disturbing the gravel produces a lot of debris, remove more of the water.

Another important point is that over the course of a week water will evaporate from the goldfish tank. It is not enough to simply top up the water. The toxic waste is left behind, and becomes more and more concentrated if the tank is only topped up.

Scrape any alga from the glass with a razor blade or credit card, then siphon off the waste water and debris. Make sure the replacement water has been treated with dechlorinator, or left in a bucket overnight with an air pump in it. Then slowly pour it into the goldfish tank.

If a goldfish is displaying the symptoms of any goldfish illness, start with a water change to see if it helps. Finally, monitor the quality of the water with a nitrate level testing kit.

Another benefit of regular water changes is that the goldfish will get used to the human contact and begin to interact when the aquarium is being cleaned.

So getting it right is important. The following checklist will enable you to make the correct decisions before digging a hole and filling it with water and goldfish.

Position

The goldfish pond needs to be in an area that gets about 6 hours of direct sunlight per day. As there may also be the need for pumps, filters and possibly UV treatment mechanisms to control algal growth, it will need to be positioned where an electrical supply can be installed. Leaves can poison goldfish, and tree roots can easily pierce any pond lining, so keep the pond away from trees as much as possible. Finally, try to site the pond in a flat area of ground.

Liner

Goldfish pond liners come in three main types: sheet, pre-formed plastic and concrete. Using a sheet offers the most flexibility in terms of shape but they are more easily damaged by rocks and roots. Preformed plastic liners offer convenience and are more durable than sheeting, but there is obviously a limited number of designs. Concrete lining is the most sturdy and long lasting, but requires a lot of work if the pond ever needs to be removed.

If using a sheet, the size required is calculated as follows: length = maximum length of the pool + twice the maximum depth, width = maximum width of the pool + twice the maximum depth. Then add a couple of feet both ways for the overlap round the edge of the pond.

Shape

The most popular shape for a goldfish pond is natural looking rounded curves, but there is nothing wrong with square, rectangular, circular or polygonal. Each of these can look visually stunning in a well landscaped garden.

The body of the pond should have at least one shelf for marginal plants, and the sides should be sloped to prevent ice getting stuck deep in the pond in winter time.

Size

The most common mistake made at the first attempt at a goldfish pond is making it too small. Larger ponds are easier to maintain because they form self-regulating ecosystems that in some cases do not need any intervention e.g. filters and pumps. The depth doesn’t need to be any more than 2 or 3 feet in most climates, but in parts of the world where it can get very cold, extra depth will be required.

Fish

The number of fish a pond can sustain is dependant on a wide range of conditions. The amount of water is the most obvious, but filtration, aeration and the size of the fish must also be taken into account. A general rule is 6 inches of fish length per 350 litres of water. Bear in mind that natural lakes and rivers do not support large densities of fish like would be seen in an aquarium.

Plants

The plants that are best for a goldfish pond are fairly dependent on the part of the world the pond is in. The best place to find out about pond plants is a local garden centre. Anacharis and water lily are usually recommended.

Following these guidelines will help make sure a goldfish pond is an attractive garden feature, and maintaining it does not cause endless headaches.