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Below you’ll find a list of the most common aquarium problems along with their causes and how you can fix them if you find yourself at their mercy.

If you’re sick of reading the old complicated beginner guides then check out our guide: Best Freshwater Aquarium Setup. Check it out!

Let’s get into it.

Water Quality Problems – How Do I Fix My Aquarium Water?

One thing every aquarist should understand is that an aquarium isn’t merely a decoration piece, and fish are not organic ornaments.

They are live pets that deserve care and consideration.

Unfortunately, poor water quality is the root of most aquarium problems and one primary reason why fish in the tank gets sick. Monitoring and maintaining water quality is imperative for your fish’s health.

Ammonia Spikes

In a fully cycled tank, the ammonia concentration shouldn’t go above zero (ideally).

Ammonia might spike if bioload in your aquarium increases, and the beneficial bacteria are finding it hard to break down all the ammonia being produced.

Other causes might include inadequate filtration, removing surfaces where bacteria grows, or even untreated tap water.

In any case, if ammonia spikes in your aquarium (goes beyond 1 PPM), the best remedy is to do a fifty percent water change. It will get rid of half the ammonia and dilute the rest in freshwater.

Please don’t feed your fish that day, since their waste and uneaten food will contribute to the problem. Most grown aquarium fish can easily survive three to seven days without food.

Do a 50% water change the next day, and recheck it.

In most cases, you’ll get it under 1 PPM in two to three days.

Feed your fish, but keep it light. Feed once if you usually feed twice. Recheck the ammonia levels, and if they are even near 1 PPM, do a 50% water change. An ammonia reducer can also help.

Further Reading: An Ammonia Spike Is One Of The Most Common Problems For Beginners. Read Our Guide To Learn How To Remove Ammonia From A Fish Tank

High Nitrates

High Nitrates, while tamer than ammonia spikes, are still one of the common problems that aquarists face.

Nitrate poisoning (gradual exposure to high nitrate levels) or nitrate shocks (sudden exposure to a high level of nitrates) are just as capable of killing a fish in a tank, as ammonia is.

The ideal nitrate range is between five and ten PPM, but in a community tank, that limit can be pushed to 50 PPM. Some species (primarily freshwater) can survive relatively higher nitrate levels, but marine fish can’t.

Live plants reduce nitrates, but it’s a long-term solution.

One of the best quick solutions is a water change, but make sure to do it in small intervals, so that you don’t stress the fish even more. A five percent change every hour is ideal until you’ve changed over half the water in your tank.

Proper aeration, live plants, routine water changes are few ways you can keep Nitrates from spiking.

Cloudy Water

One of the common aquarium problems is cloudy water.

Improperly cycled new tank, too much biomass for tank size, overfeeding (leftovers cluttering the gravel), and inadequate mechanical filtration (or wrong filter media) can cause cloudy water.

And it’s not just an aesthetic problem, murky water can create other problems for fish in tank, like irregular water parameters.

When you face the cloudy water problem when starting fish tank, usually, it’s because it wasn’t cycled properly, and now you have bacteria bloom.

You can fight that problem by vacuuming the gravel regularly, cutting the feeding, increasing bioload (reduce it if you have another tank), and making sure that filter is powerful enough.

Water changes don’t directly address the cloudy water problem, but it targets many underlying issues causing the water to go cloudy.

In an established tank, change the filter media regularly, maintain bioload in your aquarium, and vacuum regularly.

Further Reading: If You Suffer From Cloudy Water? Read Our Guide On How To Get Rid Of Cloudy Fish Tank Water

Green Water – Why Is My Aquarium Water Green?

Water in your aquarium can get green because of algae particles floating around in your water. They aren’t dangerous to the fish and plants (in most cases), but the aquarium doesn’t look good with green water.

Two leading causes behind green water is the tank of fish getting too much light, and an abundance of phosphates and nitrates in the tank (which isn’t suitable for your fish).

Nutrient imbalance can also contribute to the problem.

To get rid of the algae coloring your water (thankfully not red), you can take out some water and do a partial change.

You can also use algae killing chemicals, but they can be harmful to other live plants, so check before using. A strong UV filter also helps prevent the growth of algae.

Possible Excess Nutrients, Waste & Uneaten Food

All these elements can disturb the water parameters in your aquarium.

You can vacuum your substrate to remove all the solid particles accumulated on its surface (waste and uneaten feed).

Live plants can consume most of the excess nutrients, but if you take out a bit of water and do partial changes regularly, your aquarium water won’t accumulate too many nutrients in the first place.

Not Doing A Fish Tank Water Change Often Enough

Regular water changes are imperative in keeping your aquarium water clean and healthy for your fish.

The good idea is to combine vacuuming the gravel with partial changes. You can drain 10-20% water every week in a partial change to improve water quality, but the exact amount and frequency will depend on your bioload.

Make sure to take into account how messy your fish is. Frequent water changes can solve most aquarium problems.

Further Reading: One Of The Best Tools To Help With Doing A Water Change Is The Python Water Changer

Not Enough Beneficial Bacteria

An adequately cycled aquarium usually has a healthy amount of beneficial bacteria (and not many problems), but it can get overwhelmed if the bioload increases.

A strong presence of beneficial bacteria is vital to ensure that waste in your aquarium is processed efficiently. The biological part of your filter and your substrate and rocks are some of the places where it lives and thrives.

Additionally, bio-balls can increase the number of helpful bacteria in the aquarium by adding many more new surfaces for it to grow.

Elevated ammonia levels and fish getting sick or dying are indicators that there aren’t enough helpful bacteria in the aquarium.

Algae Growth Problems

Too much light, nutrients, phosphate, and less full or partial changes can cause many aquarium problems, including algae growth getting out of control.

But the overgrowth of common green algae is relatively benign compared to some other aquarium problems related to algae

Brown Algae

Brown Algae, also caused Diatoms, is usually caused by an excess of Silica that’s introduced to the aquarium either through tap water or silica-based/rich substrate.

Unlike green algae that stick together and can be scrubbed clean easily, brown algae are difficult to rub off from surfaces. Its presence also means that water parameters in the aquarium are upset.

The simplest way to remove brown algae is by physically removing it. You can scrub it off your aquarium walls, rocks, and even from plant leaves.

You may want to prune some leaves that have too much brown algae growth. Use RO-filtered water to refill the tank, since it doesn’t have any silica.

Also, watch the nitrate levels in your tank, and only provide light for a maximum of 6 to 8 hours a day. Introducing Nerite snails in your tank is also very helpful against Brown Algae.

Further Reading: Learn If Brown Algae In Your Fish Tank Is Good Or Bad & How To Get Rid Of Brown Algae

Red Slime Algae

Red Slime algae is not a true alga. It’s a photosynthetic bacteria called Cyanobacteria. It’s called red slime algae when it grows in marine aquariums and blue-green algae in a freshwater aquarium.

Bacteria called Red slime algae are not as harmful as brown and can even provide food for herbivore fish in your tank, but it causes problems in your aquarium is large, uncontrolled concentrations.

Like many other common problems in an aquarium, regular partial changes help with red slime, by getting rid of extra nutrients feeding its growth.

Use a powerhead or a small water jet to remove red slime algae off of rocks. Then you can vacuum if off the tank. For marine tanks, some specific Cyanobacteria removing chemicals might also be helpful.

Fish Are Dying – What Would Cause Fish To Die In A Tank?


There are several reasons why your aquarium might be turning into a watery grave.

Low Oxygen Levels – Fish Gasping at the Surface

Poor water quality is usually the most common cause.

If there is too much ammonia or nitrate in the aquarium, fix that first.

An overstocked planted aquarium might have more oxygen requirement that you are providing, so improving aeration and water movement.

The remedy is the same if the carbon dioxide levels in your aquarium are increasing to dangerous levels.

Check the pH. Acidic water can also cause the fish to gasp at the surface. You can add some benign base chemicals to maintain a healthy pH.

High temperature is another culprit, especially in summer. If your aquarium is getting too much sunlight, it will increase the temperature beyond what your fish is comfortable with, and cause a host of other aquarium problems. Sometimes, sick fish gasp at the surface as well.

Change In Fish Behaviour Or Appearance

Fish behavior typically changes when the fish are stressed.

They would gasp at the surface, not take enough food, difficulty swimming, white spots on the body, rubbing on a hard surface, tail rot/fin rot, bloating, eyes bulging – these and many more behavior/appearance change signs that your fish are either stressed or sick.

The first step to take towards countering these problems is to test water parameters. If nothing is out of the ordinary, look for signs of bullying and fighting among the fish.

If water parameters are okay and other fish aren’t bothering the sick one, remove it to a quarantine tank. If isolating it doesn’t affect the problem, then you may need to use medicine to treat the fish.

Fish Disease

Apart from worms and parasites, most common diseases your fishy friends can suffer from are due to water quality, bacterial infections, and upset parameters.

Ammonia and nitrate poisoning can be dealt with by feeding less and improving water quality. Bacterial diseases like columnaris (mold-like lesions on skin), can also be treated by improving parameters.

Fin rot and Ich (White spots or bloody streaks), and dropsy (bloating and protruding scales) need medication, mostly antibiotics. Fungus on tank inhabitants can also be caused by poor water quality, but also needs medicine to treat.

Tank Crashes

In a reef or freshwater tank, a tank crash refers to almost all or most of the inhabitants suddenly dying. When a tank is crashed or crashing, it’s usually too late to save anything.

And even if you have another tank, removing the few living inhabitants of a crashing tank to the other might not be wise as you may introduce something that causes the other tank to crash as well.

The usual course of action is starting a new tank, but a tank crash is a difficult thing for any aquarists to go through. And it can be avoided with proper maintenance, timely care, and observing problems and symptoms early on.

Worms

Worms are another one of the aquarium problems that many aquarists have trouble dealing with. They can be parasitic or commensal. They can also be outside or inside of your fish. Some of the most common types are:

Detritus Worms: Small threadlike detritus worms are very common and begin is small numbers. If your tank is seeing a population explosion, frequent partial changes and vacuuming can help you fight it.

Flukes: Flukes areSmall, microscopic worms that cause skin irritation in your fish and cause it to rub on hard surfaces. Using Praziquantel is the safest and most common method.

Anchor worm (Lernaea): They are visible on your fish’s skin, but most of the worm is inside the fish. The most common treatment includes potassium permanganate (either add it in tank water or dip the fish in it). You can also dip the fish in saltwater, formalin, or antiparasitics.

Tapeworm: Tapeworms cause digestion problems in fish, and they lose weight. The best way to treat is to remove the infected member of your tank to a quarantine tank and use relevant medicine. You can dose it in your aquarium as well, to prevent tapeworm buildup.

Thanks for reading!

This article is part of a large series of articles to help you understand the benefits, myths, cost, and steps you need to take to set up a successful aquarium.

Below are links to the next and previous chapters in this series.

Now let’s get started on setting up your new aquarium.