Questions
Questions and answers
Here are the questions beginners ask most often: in the first days after buying an aquarium, before a trip to the pet shop, and at the moment a fish suddenly starts behaving strangely. The answers are short and general, and where everything depends on the species, we say so plainly.
It's better to ask “what if…” before buying a fish than after. Most aquarium troubles begin with a hasty decision.
Water
Why is water straight from the tap dangerous?
Tap water is disinfected with chlorine or chloramine, and both are harmful to fish. Chlorine evaporates if the water stands, but chloramine stays, so you need a dedicated water conditioner to deal with it.
What is the nitrogen cycle and why does it matter?
Fish waste and leftover food produce ammonia. Beneficial bacteria turn it into nitrite and then into nitrate. Ammonia and nitrite are toxic; nitrate is less toxic but builds up and is removed by water changes.
Why did the water turn cloudy a few days after setup?
In a new aquarium the balance is still forming, and slight cloudiness is common. Don't change all the water or add things at random: watch the fish, don't overfeed, and if in doubt, ask an experienced fishkeeper.
Do I need to measure temperature and hardness?
Yes, but the right values depend on the species. Some fish like soft, cool water, others warm, hard water. Check the profile of the specific species and keep conditions stable.
Fish and tankmates
Can I keep any pretty fish together?
No. Fish differ in size, temperament and water needs. A large fish may eat a small one, and a calm fish may suffer next to a restless one. Check the compatibility of every pair of species before buying.
Why does the shop advise buying fish in a group?
Many species are schooling fish: on their own they get nervous, hide and eat poorly. In a group of their own kind they behave more naturally. The profile of each species says how many to keep.
Will shrimp and snails get along with fish?
Often, but not always. Some fish happily eat small shrimp, and some snails breed quickly. Find out in advance which inhabitants might end up as food for others.
How do I introduce a new fish to the aquarium?
It's best to keep it in a separate quarantine tank first and watch it. That way you won't pass a disease to the others. Then introduce the newcomer calmly, after matching the water temperature in the bag and the tank.
Care and health
How much food should I give my fish?
As much as they eat quickly, with nothing left on the bottom. Overfeeding is more dangerous than underfeeding: uneaten food rots, raises ammonia levels and spoils the water for every inhabitant.
How can I tell something is wrong with a fish?
Watch for lethargy, refusing food, clamped fins, a coating or spots on the body, or rapid breathing at the surface. If you see these, ask an experienced fishkeeper or a vet who treats fish.
What should I do with the aquarium when I go on holiday?
Before you leave, do a normal water change and check the equipment. Healthy adult fish usually cope well with a short break in feeding. For longer trips, ask someone to drop by and not to overfeed.
What do I do with fish if I no longer want the aquarium?
Don't release them into a pond or river: they can become invasive and spread disease, and local rules may forbid it. Offer them to fishkeepers you know or local hobby groups, or ask a pet shop if it takes animals.
Read next
- Sections
Four big topics: water and the nitrogen cycle, equipment, aquarium inhabitants and regular care.
- Guides
A step-by-step article on doing a water change without stressing your fish, plus the article catalogue.
- Reference
A fishkeeper's glossary: nitrogen cycle, nitrite, water conditioner, quarantine, schooling fish and more.
Sources
- Beginner fishkeeping handbooks
- Materials on biological invasions
Information is current as of the date this page was prepared. Fish, plants and invertebrates vary widely in their needs, so before buying a new animal, always check the requirements of that particular species.