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7 Horrible Mistakes Beginners Make With A Fish Tank

By Jake Willhoite · · Updated

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Saltwater or freshwater, these are the most common mistakes beginners make with an aquarium. Fix them and your fish have a much better chance of thriving.

Most of these mistakes lead to the same problem: poor water quality. Here are seven to avoid and how to correct them.

1) Forgetting To Change The Water

Fish waste turns into ammonia, which your filter's bacteria convert to nitrite and then nitrate. Nitrate keeps building up until you remove it with water changes.

A partial change of about 10 to 25% every week or two keeps nitrate down and replaces minerals that buffer pH. Treat new tap water with a dechlorinator first.

2) Overfeeding Your Fish

Uneaten food sinks, rots and releases ammonia. University of Florida researchers note in Ammonia in Aquatic Systems that feed is the main source of ammonia in most systems.

Feed only what your fish eat in a couple of minutes, once or twice a day, and choose food suited to each species.

3) Neglecting To Clean Or Replace The Filter

The filter removes debris and houses the bacteria that break down ammonia. Clean it on a regular schedule, following the manufacturer's directions for your filter type.

Rinse sponges and biological media in old tank water, not tap water. Chlorine in tap water kills the beneficial bacteria. Replace cartridges one at a time rather than all at once.

4) Forgetting To Check The pH Level

pH measures how acidic or alkaline water is, on a scale of 0 to 14. Different fish prefer different ranges, so choose species that suit your water.

Most common community fish do well between about 6.5 and 7.5. Stability matters more than an exact number; sudden swings stress fish and can kill them.

5) Overstocking Your Aquarium

It's tempting to buy every fish you like, but each tank has a limit. Many fish grow much larger after you bring them home, and some become territorial when crowded.

Research each species' adult size and temperament. When in doubt, keep fewer fish.

Add new fish slowly. UF/IFAS recommends a quarantine of at least 30 days for new fish, since they can carry parasites like ich without showing signs.

6) Not Testing The Water In Your New Aquarium Or Not Testing It On A Regular Basis

You can't see ammonia or nitrite in the water. UF/IFAS notes that ammonia is colorless and odorless even at toxic levels, so testing is the only way to know.

A new tank needs to cycle before fish go in; UF/IFAS says a new biofilter takes about six to eight weeks to establish. Test ammonia, nitrite and nitrate weekly, and right away if fish act strangely.

7) Overcleaning Your Aquarium

Cleaning is essential, but the beneficial bacteria that break down waste live in the filter, gravel and decorations. Wipe them all out at once and ammonia can spike.

Don't replace all the water, scrub every decoration or wash all the filter media in tap water on the same day. Routine gravel vacuuming during a partial water change is fine and helps remove waste.

Those are the 7 main reasons fish tanks fail. Follow these points and your fish should have a healthy, stable home for years.

Other possible points to consider:

  • Leaving the aquarium light on all the time.
  • Topping off for evaporation instead of doing a water change.
  • Insufficient cover provided for your fish.
  • Buying a filter that is too small.

Aimed at beginners:

  • Buying fish the same day as the aquarium.
  • Buying a fish tank that is too small.

Sources

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