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The basics

Fishkeeping isn't really that difficult, as long as you follow a few simple rules. In this section you'll find all of the basic info you need to know about maintaining a successful aquarium, as well as links to relevant beginners' articles elsewhere online and links to our massive selection of handy fishkeeping calculators.

Water changes

• We recommed changing 25% of the water every week or two. But you may need to change more water, more often if you keep larger, messier fish or have a heavily stocked tank.
• If your tank suffers from algae, or your fish get unwell, you may not be changing enough water.
• Compare the nitrate level in your tapwater to the level in your tank. If you're doing plenty of maintenance they should be about the same. If you're not doing enough maintenance, the nitrate level in the tank will be much higher.
• Use a gravel cleaner to syphon out dirty water from within the gravel whenever you do a water change.
• To calculate how many water changes you need to make, use our unique Water Change Calculator

Tapwater

• Never use tapwater without treating it.
• Untreated tapwater contains toxic chemicals, such as chlorine, that can harm fish and kill filter bacteria, leading to a rapid deterioration in water quality.
• Some water authorities use chloramine, instead of chlorine, which is much more dangerous to fish and harder to remove.
• It's safest to use a dechlorinator capable of neutralising chlorine, chloramine and ammonia, before adding any water to the tank.
• Don't rely on the old-fashioned method of aerating water, or leaving it to stand or age before adding it. Neither technique will get rid of chloramine, which is becoming much more common in UK tapwater.
• Always wash filter media in old tank water and never under the tap.

Stocking

• Overstocking leads to poor water quality, fish diseases and can kill.
• Base fish lengths on the average adult size of the fish, rather than their current size. Otherwise the tank will become overstocked as they grow.
• To calculate the volume in gallons, multiply the length in feet by the depth in feet by the width in feet and multiply the result by 6.25. To convert this to litres, multiply the result by 4.55.
• To calculate the volume without doing any maths, use our aquarium and pond volume calculator.
• Tropicals: 1" per gal./2.5cm per 4.55 l. initially, then 2" per gal./5cm per 4.55 l. after six months.
• Coldwater: 1" per gal./2.5cm per 4.55 l.
• Marines (fish and inverts): 1" per 4 gal./2.5 cm per 18 l.
• Marines (fish only): 1" per 2 gal./2.5cm per 9 l.
• Ponds: 10" per 100 gal./25 cm per 455 l.
• To work these out online, use our stocking density calculator.

New tanks

• Tanks that have been runing less than a couple of months need careful monitoring and light stocking.
• Filter bacteria, which remove harmful pollutants in fish wastes and decomposing food, usually take 4-6 weeks to grow, so during this time the water can become dangerously polluted.
• Test regularly for ammonia and nitrite and carry out partial water changes of 30% (or up to 50% if necessary) to keep levels under control during this period.
• Don't add any fish until the water is completely free of pollution!

Buying fish

• Some fish have specific water quality and habitat requirements. Read up on any new fish before buying it to ensure you can meet its needs.
• Always test your water for signs of ammonia and nitrite, and ensure the nitrate level is low. New stock may die or become diseased if added to new water.
• Determine how much space is available using a simple stocking density calculation. Do not overstock your tank.
• Only add a few fish at a time, and leave a week or two between each new addition.

Adding fish

• Try to get new fish home as quickly as possible. Keep them somewhere warm, dark and quiet on the journey.
• Turn off the tank lights and float the unopened bag on the water surface for five minutes.
• Open the bag by undoing the knot, or cutting the knot off. Do not pop the bag.
• Roll down the neck of the bag to make a collar so it can float unaided.
• While fish do take a long while to truly adjust to changes in water chemistry, adding some water to the bag can help make the transition less stressful. Add a cupful of water every five minutes for 45 minutes.
• Turn the bag on its side and allow the fish to swim out. Leave the lights off for a few hours and keep an eye on the new fish.