Cold Water Fish Care Guide

It can be more difficult than you’d imagine looking after a fish. They may be one of the cheapest pets to care for, but if you don’t get everything right, your fish won’t have a happy, healthy life.

There are three types of pet fish – temperate, cold water and tropical water. Luckily, if you’re keeping cold water fish, you don’t have to do much extra such as having heaters.

Despite this being a general rule, every individual breed does need specific requirements.


  • Lifespan: ~5 Years
  • Average Size: 1-7cm
  • Average Weight: 150-300g
  • Popular Breeds: Goldfish, Tetras, Barbs, Loach
  • Diet: Depends on the breed. Flakes and pellets are available
  • Water Temperature: 15° to 30°C


  • You can treat fish like any other pet – annual vet trips and regular checks are still recommended, but you may have to go to a specialist
  • Coldwater fish don’t need many additions to their tank, so are relatively inexpensive to keep. You will still need filters, thermometers and dedicated fish food
  • How many you can have depends on the breed – tetras fight so usually need to be kept alone, but many other breeds need to be in schools
  • You should get a tank of the generous size when it comes to capacity – a fish tank can’t be too big. It also needs preparing around one week before you bring your fish home
  • You can handle them by net catching but you must do this as little as possible – only if they need care or you’re cleaning their tank fully


Aquariums are your best bet. They are a common part of many towns and cities. Pet shops are another possibility, as are chains such as Pets At Home.

You should always check that the shop has a suitable setup, paperwork and notes on the fish they keep to ensure they’re a reputable seller. Ask the seller plenty of questions regarding the fish, and you’re best buying if they are knowledgeable.

The healthier a tank set up is, the better chance that your fish are healthy

Fish breeders are also available, but this will usually be with specialist fish such as Siamese beta fish.



  • A healthy fish should be active and able to swim through the water easily
  • Scales should be shiny and full of colour and cover their entire body with no gaps or cuts
  • If a goldfish gasps at the surface of the tank or swims in a peculiar way, then don’t buy it. Sluggish movement and drooping fins are a sign of illness


If you buy a fish from the original breeder, there should be notes on birth dates and age. Young fish still need plenty of space to grow in size, so buy a generously sized tank. Also, understand that their birth date may not be absolutely spot on because it can be hard to spot exactly when fish are born. There is no guarantee how long they will live for, either

You can sometimes tell the age of a fish by looking at their scales, but it is different for every breed


For most breeds, a mixed tank of males and females will be fine. Although this could mean breeding and fighting so most recommend that single-sex tanks are the best. Sexing a fish can be hard, so if you buy a female there is no guarantee that it is 100% a female – always watch for behaviour and tank issues with any new fish


Fish can’t be cuddled like a dog or cat, as we all know. They also need to be kept in water. So, your handling will naturally be kept at a minimum.

You may need to remove them from the tank if they are ill, or if there is fighting in the tank. You can also remove them when you are carrying out a thorough clean of the tank (such as gravel and decor), around once per month.

To remove them, use a net. Ensure you do this slowly yet securely, so as not to scare or injure them. Place them straight into a tank of suitable temperature water

Having a spare small tank you can prepare in plenty of time is a good idea



As mentioned, get a tank as large as possible. Fish can’t really have a tank that is too large but they can be too small. Ensure you have a thermometer to monitor the temperature, as well as filters and plenty of decoration to give them space to hide. They should also have a suitable substrate at the base – we like gravel but you may need soil if you have plants

How To Look After Goldfish Cold Water Fish


Tanks should be cleaned in different ways both daily and weekly. Deep cleans need to be done monthly.

Every day, clear uneaten food with a net.

Weekly, clean the glass of the tank and any algae, remove 20% of the water and treat the replacement water, and carefully add to the tank. Never replace the water entirely unless asked to by a vet because there is a health issue.

Monthly, a tank should be deep cleaned if it seems to be getting dirty, such as the gravel. You may have to take your fish out of the tank for this, but in some cases, they can be left


As with other fish types, every breed is different.

When we say ‘coldwater’ we don’t mean cold drinking water that humans have – it is more the temperature of standard lukewarm water or the temperature of our homes. 15° to 30°C is usually a good guide, but it is important to get as close to their ideal temperature needs as possible

Bear in mind external temperatures too – never put a tank near a heat source or window


Again, it can alter. Goldfish like a pH of 7.0 to 7.5, and Neon Tetra is 5.8 – 6.2. Tiger barb is similar to tetra. Always research for your particular fish breed, and ensure this is checked regularly


Fish themselves don’t really need lighting, but the plants in their tank are the main benefactors. Get the right level of lighting, and you may also benefit from a timer so they can have darkness at night.

Remember that lighting can also make your tank and fish look great, which is important if you’re going to be appreciating them to look at.

For best results, use fluorescent bulbs, compact fluorescent bulbs, metal halide lights, or LED lights. Avoid incandescent bulbs as they are suitable only for small aquariums and give off too much heat. Coldwater fish don’t have to be overly illuminated, so anywhere in the region of 8 hours of light is adequate.

In large or deep tanks, intensity is really important


There are dozens of types of substrate available for fish. Which is best depends on their behaviour and tank needs.

For instance, if they burrow they will need something quite soft such as sand. The same can be good for bottom feeders as the food which falls will be easy to access. Fish that lay eggs regularly would benefit from stones as they won’t be able to find and eat the eggs once they fall.

Plants can benefit from soil substrate and large stones can also keep plants in place. In a lot of cases, several different substrates can be used, for a natural and practical look but they have to all be safe. Research the best for your particular breed

Other Products Needed

Fish will benefit from small houses and other areas in which they can hide during the day or sleep. Plants also work in the same way.

Then, of course, you also have your filter, pH checker, and temperature thermometers. The latter isn’t as crucial for cold-water fish as the water should keep at a standard natural temperature anyway, but in the very hot or very cold months, it could show if there are any signs of variation or any issues



Fish can eat pellets or flakes. The main thing is to research how they feed – bottom feeders need food that will sink, and top feeders a food that will float. You can get food specific to certain breeds, such as goldfish or tetra, which contains everything that particular fish needs.

Most cold-water fish just eat plant-based flakes but check whether yours also needs food such as bloodworm

Common Issues With Diet

Overfeeding is more dangerous for fish than underfeeding. You should feed a small amount twice per day, and only give as much as they can eat in 5 minutes. Any extra food lying about can cause the tank to get very dirty.

Also, ensure that the food is as perfect for your fish as possible. If you’re not sure, buy breed-specific or dedicated cold water fish food flakes.

Fish can be carnivores, herbivores or omnivores. Getting the right diet is essential

Foods To Avoid

Just feed their dedicated feed. Don’t give them a bit of your leftover toast or roast beef! Fat for fish is very bad unless yours is a carnivore in which case you should limit fat to 6% daily.

Some people say that you can feed herbivorous fish blanched lettuce, peas and spinach, but in a lot of cases they will likely turn their noses up at it if they’re used to protein-rich flakes and pellets. Stick to their usual unless you have been advised by a vet to change it up a bit

Tips For Feeding

As mentioned, only give them as much as they can eat within 5 minutes twice per day. Just drop the food into the tank, preferably over an area that will make it easy to access

Looking After Cold Water Fish


Health Checks

Check your fish every day and see how they swim, whether they seem to have changed their behaviour and if there are any signs of bullying in the tank. A change in scale condition and colour can also be a sign something is wrong.

Just as with larger pets, taking your fish for an annual vet checkup is a good idea. This is usually done with larger fish or solitary/specialist breeds, but some can look over a school of fish too

Veterinary Care

Fish don’t need annual booster injections or microchips. They should get all they need health-wise from their food and a clean tank of water. It is a good job to register with a vet in case you do need to take them in, or if you need some advice over the phone just.

Many local vets will usually be happy to do this, but you may need to go somewhere a bit more specialist if not. Vets can also prescribe medication for some of the below issues, such as cottonmouth

Most fish medication will be added to the water, so if the whole tank doesn’t need treating, you will have to separate them

Common Issues

The majority of health issues with fish are caused by dirty water, so it is vital to keep on top of this. In most cases, the same illnesses affect fish no matter what breed or conditions they’re kept in.

It isn’t a disease, but ammonia poisoning can be rife. It causes stress and leads to other health issues too. Murky water and fish gasping at the air are two clear signs.

Cottonmouth affects cold-water fish. White or grey patches appear on their head. It is a bacterial infection, so they can soon face issues with their skin such as lesions. Dropsy is shown by a swollen abdomen and is often fatal unless they are quarantined and you seek vet help ASAP.

Fin/tail rot can be caused by bad water quality or pack bullying. Unsurprisingly, it looks like their fins or tail are fraying. Again, antibiotics can help.