5 Signs of Trouble in Your Aquarium

Okay, so ideally you should have an array of equipment, charts, and potions that allow you to assess the health of your aquarium. Things like water test kits, thermometers, and a regular maintenance schedule are critical to keeping your aquatic pets happy and healthy. But sometimes one or more of these tools aren’t available, or you might be new to the hobby, and just don’t know what’s going on half the time. If you are new to the hobby, you should consider reading my articles on water parameters, aquarium filtration, the nitrogen cycle, and tips for beginners.

Okay, you’ve read the articles, and would now like to get on with it! So what are some signs to look for that indicate things might be going wrong? Below is a list of five things to look out for:

1. Sudden Color Shift in the Water

One of the first obvious signs of something going on in your aquarium is if the water suddenly seems to take on a new color or “thickness.” This isn’t always a sign of danger ahead, but it should give you cause to investigate the source. You may find that your water has one or a combination of these color types:

Green Water – A green color cast to your aquarium water usually means one thing: algae bloom. The color comes from millions of single-celled algae. They tend to explode in number when there are excess nutrients and abundant light in the water. If left unchecked, the green color can quickly thicken, making it impossible to see through to the back of the aquarium. No amount of water changes will be enough to get rid of it for long. Luckily, I have written a handy article for how to treat this and other common types of algae.

Yellow Water – Yellow water is often caused by there being a lot of organic compounds dissolved in the water. These come from lots of sources, like fish food, fish waste, broken down plant matter, etc… This isn’t necessarily harmful to your pets, but it can cause a few problems. If you have a lot of plants in your tank, the dissolved particles will block some light from reaching the leaves. These compounds also bind with necessary nutrients in the water, preventing your plants from accessing them effectively. Yellow water can also lead to green water or milky water, because microorganisms can take advantage of the dissolved organic compounds to explode in number. You can remedy this by simply conducting scheduled water changes and perhaps some gravel vacuuming to remove any excess nutrients leeching out of the substrate.

Brown Water – Brown or Tea Colored water is caused by tannins. They generally come from driftwood decorations that are new to a tank. There are those that would not consider this a bad thing. Some hobbyists encourage this kind of water for what are called blackwater aquariums. These aquariums are an attempt to emulate natural waterways found in heavily forested regions. Tannins are what’s leftover when certain plant compounds break down. One of those compounds is lignin, which is what makes wood so sturdy. When those lignins break down, tannins are what’s left. Tannins are what gives tea or spirits that familiar brown color.

Tannins are not harmful to your pets, in fact some species benefit from their presence in the water. But not everyone appreciates the blackwater look. If you suddenly find yourself with brown water, it is probably from that piece of driftwood you added to the tank a few days ago. You can minimize this by boiling your wood before adding it to the tank. Find an old pot that you can submerge the piece of wood into, fill it with water, and boil that sucker for a few hours. The water will turn dark brown. Repeat this process until the water is a much lighter in color or even clear. Let the wood cool and put it back in your aquarium. If some tannins still continue to seep into the water, just keep on with your regular water change schedule. The brown color should clear up over time.

Milky Water – Milky water is another sign that isn’t necessarily bad. Many tanks are cloudy or milky when they are first set up. Assuming the cause isn’t silt from your new unwashed substrate, the cause is usually a bloom of bacteria in the water. As a tank cycles and becomes settled into a stable balance, there can be an excess of nutrients and bacteria in the water column. If you continue your maintenance schedule this should clear up on its own.

If however, cloudiness suddenly occurs in an older aquarium, this could be a sign that something in the environment has changed, resulting in a bacterial bloom. This could be caused by a big water change, forgetting to use dechlorinator, changing filter media, or even a change in the amount or type of food you are feeding your pets. You should try to identify the cause, just incase it is something that you need to correct, like a dead fish behind the plastic castle. If the milkiness is so thick that you are having trouble seeing inside your aquarium, then you got some finding out to do!

2. What’s That Smell?

Another sign that can alert you to a potential problem in the works is how your aquarium smells. What? You’ve never given your tank a sniff before? You should. We can learn a lot about the health of our aquariums by becoming familiar with how a healthy tank smells. This way, you can be alerted immediately if something is off.

First, if you have an average size aquarium (let’s say 20 gallons) in a typical size room (let’s go with 10 feet by 10 feet), you should not be able to smell it when you first enter the room. A healthy tank should not fill a room with “fish smell.” If you have many tanks or a really small room you may be able to smell their aroma, but otherwise you should need to get within a couple feet before it hits you.

When you do catch a whiff, a healthy tank should faintly smell somewhat like a lake or stream. If you have soil as part of your substrate, it should have a somewhat earthy or “woodsy” scent. Again, it should be mild and only noticeable from very close to the water surface. Every tank is set up differently, and yours may not smell exactly like the next hobbyist’s, so you should become familiar with how your tank smells when things are good.

If you aquarium smells like rotten eggs, burnt popcorn, or an intensified “fishy smell,” but is still only noticeable within a few feet of the aquarium, then it’s a sign that you should probably examine what may have changed to cause this. Have you been using a different food? Is one of your fish missing? Has the filter stopped working efficiently? It may be something that’ll go away on its own, or you may need to handle it yourself.

The rotten egg smell is not necessarily a bad sign. It could mean that some sulphur dioxide has escaped from deep within your substrate. Sulphur dioxide is produced by anaerobic bacteria that often live in the substrate. It’s a gas that you don’t want a lot to your pets, but if a few bubbles here or there emerge now and then, you should be okay. You may want to use a stick or something similar to occasionally poke into your substrate, to help dislodge a few bubbles with your regular maintenance. This will prevent a large pocket of gas from forming and potentially releasing all at once.

If you suddenly notice a stronger fishy smell that wasn’t there before, it could be caused by fish stress. When fish are stressed, they can actually give off a different smell than usual. This new scent is caused by heat-shock proteins. So if you are suddenly noticing an intensified fishy smell, take a close look at your pets to see if they are showing any unusual behaviors or if they look ill.

If your tank has an intense, nauseating scent, like burning rubber, this is a bad sign. It’s a huge red flag if you can smell it, when you first walk into the room. Something has definitely gone wrong. A fish or invert may have died and is now rotting, or your filter has stopped working. It could mean there’s rotting food somewhere in the tank. Whatever the cause is, you should identify it ASAP. I would recommended doing an immediate large water change along with identifying and removing the cause.

3. Changes in Pet Behavior

If you watch your fish, they’ll let you know when they are unhappy. If the smell is good and the color of the water is good, but your fish are showing signs of stress, then you’ve got a problem. When assessing fish behavior for signs of stress, look for: clamped fins, gasping for air at the surface, hiding behind equipment, not eating, or positioned unnaturally in the water (upside down or tilted). All of these behaviors indicate something is wrong.

If a fish is gasping for air at the surface, it could mean there is too little oxygen in the water or that the water has a high concentration of Nitrites. If the fish has its fins tightly clamped against its body or it is suddenly hiding behind decorations or equipment, this can mean lots of things like being picked on or feeling ill. If your fish is hanging awkwardly in the water, either upside down or tilted to the side, this too can mean different things, for example something wrong with its swim bladder.

Your invertebrate pets can also give you warnings about your aquarium. If your snails are all hanging out at the water surface, this could be a sign that the water parameters are unfavorable to them. This is also true if the snails completely exit the water. Some snails do this to lay their eggs, so it isn’t always a bad sign. However, snails like ramshorns or malaysian trumpet snails should have no reason to leave the water, unless there is a tasty mat of algae calling out to them.

If your snails are stressed, they will often spend long periods of time closed up inside their shells. This is because in the wild, a snail’s first defense is to clam up and wait for danger to pass. In your aquarium, if the water quality is poor, your snails may do this for extended periods of time, hoping that conditions will change on their own. In this way, even if the stressor isn’t directly fatal to the snail, they could starve to death, because they do not leave their shells to feed.

Crustaceans like shrimp and crayfish can also signal to you that something is wrong. Normally, shrimp will constantly graze on algae and biofilm in your tank. If they are instead spending long periods of time just sitting there, not eating or cleaning themselves, then this could be a sign that something is wrong. Crayfish can also be seen to become lethargic and even roll over onto their sides or back. They may also do this when attempting to molt, so do not panic. Observe your pet to determine if this is the case.

4. Colors, Fins, and Sores (Oh my!)

As with your pet’s behaviour, you can clearly see something is wrong when they are exhibiting physical symptoms of illness. When a fish is ill or stressed, often its colors will become muted or pale. This also happens when fish are sleeping, so do not panic if you see they are a bit pale in the morning when the light first comes on. However, if your fish is consistently less colorful than it once was, this could be a sign that something is amiss.

If your fish’s fins are showing signs of fin rot, then you absolutely have a problem on your hands. Fin rot is caused by poor water quality. This is a common affliction among Betta fish and goldfish, because they are notoriously mistreated by young and inexperienced fish hobbyists. If you catch it early enough, and make drastic changes to your maintenance and the environment your pet lives in, he or she can recover in time.

Finally, if your fish have obvious sores, blisters, or polyps on their skin, fins, or gills, then there is either an environmental problem or your fish has contracted a parasite or other pathogen. Ich is a very common affliction for fish, and is characterized by white dots on the skin. An infected fish will also try to relieve its discomfort by rubbing up against decorations and equipment in the tank.

Cory from Aquarium Co-op has a few great videos on treating fish illnesses. Here is one below:

5. My Plants Are Melting!

Like with your pets, your aquatic plants can tell you a lot about how your tank is doing. Plants too have standards for water quality. If your plants start dying back, melting, or turning funky colors, then something could be up. It may simply be that your plants are lacking in some nutrients, but it could also mean that your aquarium has bigger problems brewing. Check out my article on aquatic plant nutrition to help diagnose some problems you may encounter.


Well, I hope this list is helpful to you. If you are just beginning in the aquarium hobby, chances are you will make some mistakes. It’s just part of the learning process. You can minimize those mistakes by following some basic aquarium care techniques. The first thing is to obtain and learn to use the equipment necessary to maintain the health of your tank: a thermometer, water test kits, and medications. Lastly, come up with a structured maintenance schedule that works for you and your tank.


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