Care & Maintenance

The secret to successful fishkeeping is to look after the water. If you provide fish with good quality water with the correct chemical parameters, they will almost certainly thrive.


There are 3 aspects to filtration.

Mechanical, straining out fine particles of dirt & debris which would otherwise make the water appear cloudy or hazy.

Chemical, the use of chemicals such as carbon to remove dissolved impurities which discolour the water, or fish treatments when a course of treatment finishes.

Finally & most importantly, biological filtration. This is the process whereby bacteria living in the filter break down organic waste produced by the fish, decaying plants, uneaten food, etc.

This waste is in the form of a highly toxic chemical, ammonia. In a mature filter, with a healthy population of these beneficial bacteria, any ammonia in the water is rapidly broken down, firstly to nitrite, which is also toxic, and then to less harmful nitrates.

Once a reasonable colony of these bacteria are established in a filter they can rapidly multiply to cope with the additional waste produced when new fish are added to the aquarium. However when a tank is first set up it can take several weeks or even months for the bacteria to become properly established.

Adding too many fish too soon to an aquarium can therefore result in very high levels of ammonia and/or nitrite building up to a point where the fish are harmed or even die. Although it is possible to mature a tank by adding a few ammonia tolerant fish and waiting for the filter bacteria to establish, a far better method is to establish the bacteria before any fish are added.

There are various ways this can be achieved, but the method we recommend is as follows.

Firstly, set up the tank with gravel, rocks & other decorations and fill with treated (dechlorinated) tap water. Turn on the heater, filter & lighting and leave for at least 48 hours.

Next add plants plus Tetra “SafeStart”. SafeStart is a culture of the necessary filter bacteria, alternatively, if you already have an aquarium, or have a neighbour or friend who has one, gently rinse some of the filter media from the established tank in a container of their tank water, and pour the resulting brown “soup” into your new aquarium or filter.

Finally wait patiently. If you have your own test kits, monitor the ammonia & nitrite levels, if you see a rise in either, wait until both have come back down to zero before adding any fish.

Alternatively if there is no rise in ammonia or nitrite after two weeks you’re safe to start stocking with fish.

If you don’t have your own test kits we’re happy to check the levels for you. Ideally wait at least 2-3 weeks and bring us a water sample in a clean jam-jar or similar container. Once you start adding fish, don’t add too many too quickly, and make sure that the water quality remains good before adding the next batch.


Although the nitrates that are the end product of filtration are less toxic than ammonia or nitrite, if allowed to build up in the aquarium they can encourage algal growth, and at high levels they’re also toxic to the fish.

To some extent the nitrates are used up by the plants, but it’s important to get into a regular routine of water changes in order to keep the nitrates to acceptable levels.

Each week, if there is any build up of algae on the glass of the aquarium, this can be removed by use of an algae magnet, aquarium scraper or even a hand held pad or wad of filter wool.

Next use a gravel cleaner/syphon to remove about 10% of the aquarium water, by moving this through the gravel, silt and sediment can be removed from the aquarium before it decomposes and produces more nitrates.

Refill the aquarium using tap water which has been warmed to approximately the same temperature as the aquarium with boiled water from a kettle (don’t use hot tap water as this potentially may contain high levels of copper, which can be toxic to fish). Treat the water with a declorinator such as Aquasafe to neutralise the chlorine before adding it to the tank. Don’t be tempted to change too much water, usually 10% weekly is more than adequate, but if necessary 20-25% at a time is OK. If you feel the tank needs a larger change, you’re better off doing a series of daily 20% changes, rather than one big one. The reason for this is that the larger the water change, the greater the risk that some aspect of the water quality, temperature, pH, etc. will swing so drastically that it will upset & kill either the fish, or the filter bacteria

Cleaning your filter

The important thing to remember about your filter is that it’s home to your filter bacteria and you don’t want to kill them! Obviously, the exact maintenance procedure will vary for each model of filter, but there are some good basic principles that apply to all.

1. Only clean the filter when it needs it. This is especially true for the biological part of the filter, the more frequently you clean the filter, the more likely you are to kill your beneficial bacteria.

2. Never wash the biological part of your filter in tap water, the chlorine in it, is intended to kill bacteria. Instead, if the biological media is becoming clogged with dirt & debris, wash it gently in a bowl of aquarium water, the water removed during a water change is ideal for this. Don’t over clean, just rinse the worst of the debris off. If possible keep some of the filter media back, unwashed, and mix back into the washed media afterwards.

3. Some internal filters use a single sponge for both mechanical & biological filtration, eventually these become saturated with dirt and it becomes necessary to replace them. The best way to do this is as follows ;-
I. Rinse the old sponge in a bowl of aquarium water as usual.
II. Rinse the new sponge in the same water, this will hopefully seed it with bacteria.
III. Cut the old sponge up and squeeze parts of it into the canister with the new sponge, this should ensure that some active bacteria remain in the filter.
IV. Keep feeding to an absolute minimum and monitor ammonia & nitrite levels closely for the first few weeks after a filter change.
V. Many filters these days have multiple sponges, if so, never change all the sponges at the same time, instead after replacing one, leave at least a month gap before replacing the next.


Especially in the first few weeks, it’s important not to overfeed your fish. Fish need far less food than most people imagine, ideally feed once or twice a day, but don’t worry if you miss the odd feed, and don’t be tempted to feed extra if you do. For a typical community aquarium a few flakes finely crumbled at each feed, is sufficient to keep a dozen or so small fish hale & hearty.

For most fish, a simple diet of a quality flake food is all they need, but we do offer a range of treat foods, which can help to enhance colours & get the fish into breeding condition. Fancy goldfish such as orandas, fantails and moors are an important exception. These fish are very prone to indigestion especially if they swallow air whilst feeding on floating foods like flakes. For this reason we strongly recommend that fancy goldfish are fed on sinking foods such as Tetra Gold Japan & Hikari Cichlid Gold.



Missing a water change or two whilst on holiday is unlikely to cause problems. In the run up to leaving for the holiday it’s a good idea to do a couple of extra water changes, clean the filter a couple of days before you leave, and check that equipment like filters and heaters are all working correctly. Ideally plug the light into a timer so that it comes on & off as usual.

Fish can survive a surprisingly long time without being fed, most will be happy for two or three weeks without food. If you are anxious about not feeding your fish whilst away, we do stock holiday foods which can simply be dropped in and left, but these run the risk of overfeeding and polluting the water, if not used with great care.

There is a similar problem with asking relatives and neighbours who are unfamiliar with fishkeeping to feed fish as they will often be tempted to overfeed. One way around this is to put a single portion of food into a clearly labelled pot or envelope, and hide the rest of the food!

Alternatively we do stock a range of automatic fish feeders which can dispense food on a daily basis. If using one of these, set it going about a week before you depart so that you can monitor, and if necessary adjust, the amount of food it delivers.

If away for long periods, it’s certainly a good idea to have someone pop in and check that all is well with the aquarium and if necessary replenish the automatic feeder. On your return, carry out a couple of extra water changes and if necessary clean the filter before settling to a normal routine.

Need advice? Contact us.

If you're feeling overwhelmed by the choices or just need some expert advice, don't hesitate to reach out. Our team of aquatic specialists is here to guide you every step of the way.