Tiny Bugs in Aquarium – Causes & Solutions

Disclosure: I may earn a commission when you purchase through my affiliate links. As an Amazon Associate I earn from qualifying purchases. – read more

A well-cycled and stable aquatic ecosystem is teeming with life on all levels. Some of the life forms dwelling in your tank are visible with the naked eye, while others are not. Today, we will be focusing on both and discussing those tiny bug-like creatures that float and infest your aquarium.

Some of these are harmful, while others are benign and make for good food for your fish fry and other smaller fish species. So, let’s get to it!

Types of Bugs in Aquarium

The following are the most widespread water bugs in the aquarium world:

– Water Mites

Water mites refer to several microorganisms, including amphipods and copepods. But it’s the amphipods that fit the description the most. These are microcrustaceans similar to shrimps in functioning and even appearance. The animal looks like a typical flea, which is why it’s also known as beach flea.

You will most likely be able to observe amphipods with the naked eye, given that they grow up to ¾ inches when mature. Most specimens tend to be white but can also come in several other colors, like light brown and green. All amphipods turn red when dead.

Typical aquatic amphipod species produce one brood during their lifetime, although some species, like the Hyalella Azteca, produce up to 15 broods over a period of 5 months. Amphipods complete their life cycle in less than a year and can multiply considerably.

Fortunately, one of the only downsides of dealing with an amphipod invasion is aesthetical. The water will be teaming with these little organisms, creating the impression of a dirty and improperly maintained ecosystem.

Which may very well be the case. The animal can even clog the filter in extreme amphipod invasions due to its large numbers.

– Copepods

Copepods are widespread in a variety of ecosystems, from freshwater bodies to hypersaline ecosystems, as there are literally thousands of species and subspecies of copepods that we know of.

These adaptable microcrustaceans are similar to amphipods in terms of biology, but they’re different in appearance and size. The typical copepod may reach up to 17 mm, depending on the species.

Copepods are generally white or transparent and may come with reddish or brownish hues and long head antennae. They are very active, spread fast, and are generally beneficial to the ecosystem.

The main reason is that they consume detritus, which contributes to the ecosystem’s chemical stability. They can also serve as food for many fish species, which is why you’re unlikely to notice a copepod invasion in your fish tank.

Copepods are more prevalent in shrimp tanks since shrimp don’t eat them.

– Detritus Worms

Detritus worms are some of the most notorious aquarium worms available. They can grow up to 1 inch when fully mature and can cause panic among more inexperienced aquarists. A thick population of wiggly detritus worms never makes for a calming and relaxing sight.

Fortunately, these organisms are generally harmless. The typical detritus worm is white and lives in the substrate, out of sight. If you notice free-floating detritus worms, you most likely have ten times their number crowding inside the substrate. The worms’ presence is an indicator of poor water conditions, given that these animals are known as detritus eaters.

The dirtier the tank, the better the detritus worms will fare. Don’t worry, they’re not dangerous and may even serve as food for various fish species.

– Limpets

Simply put, limpets look like transparent microclams. Limpets can reach 15-60 mm in size, depending on the species, and can spread fast. They feed on algae, so it’s natural for them to overpopulate algae-infested ecosystems. Fortunately, they are neither harmful nor widespread.

Unlike copepods and other water mites and microorganisms, limpets do not evolve naturally in a closed aquatic system. Any limpets that get into your tank do so via hitchhiking. More specifically – via infected plants, decorations, or even contaminated water when transferring newly-bought fish into the main ecosystem.

Fortunately, limpets are quite easy to counter and remove from the ecosystem simply by tampering with their food source. Keep the aquarium algae-free, and you won’t have any problems.

– Hydras

Finally, we’re moving on to a more dangerous aquarium inhabitant, the infamous Hydra. This micro-hunter is a polyp consisting of a solid foot, and jelly-like tentacles that poison and paralyze potential prey upon touch.

Depending on the species, the Hydra can get as large as 1 cm with 2-cm-long tentacles. This turns this animal into a dangerous predator, although it can only consume very small prey.

Unfortunately, this includes fish and shrimp fry, making Hydra a palpable danger to the ecosystem. You can detect the Hydra with the naked eye and even observe its progress as it grows and multiplies.

A handful of Hydra won’t impact the aquarium much, especially if you don’t have any small fish fry to worry about. Hydras will feed on the tank’s microfauna, including copepods, water mites, various worm species, etc.

Hydras also grow asexually, so you only need one to experience a full-aquarium invasion shortly.

– Planaria

Due to their increased mobility, these flatworms are at least as dangerous as Hydras, if not more dangerous. An adult planaria worm can reach 0.6 inches and navigate the entire tank for food.

Depending on the subspecies, the typical planaria worm is white, brown, or even black. You can recognize the worm by its arrow-shaped head, which may be more difficult to detect, given that these worms change shape quite often.

They also change color based on what they’re eating, which can make things even more confusing. These animals move similarly to snails, dragging their bodies across the tank’s walls and other surfaces. They leave a thick slime behind, which contains a toxin that can kill shrimps and snails. Fish are at lower risk, given that planaria worms don’t swim.

But these animals rank as predators and have a preference for shrimp and snail eggs. Larger specimens are also known to consume baby shrimp and even attack adults. The worm may not kill the adult shrimp directly, but the poisonous slime might.

Needless to say, these worms have no business being in your tank.

How do Bugs Get in a Fish Tank?

The answer depends on the bug species we’re discussing. Amphipods and copepods are generally widespread in any aquatic ecosystem, no matter how hard you would try to avoid them. It’s only a matter of managing their numbers properly to prevent a full-on invasion.

Other organisms like planaria, Hydra, and limpets are known hitchhikers, using live plants, rocks, and even infected fish as vehicles. How you prevent and deal with these pests depends on their method of infection and overall exploitable weaknesses. We’ll get into that shortly.

Are Tiny Bugs Dangerous to Fish?

Once again, the answer depends on the bug’s nature and behavior. Copepods and amphipods are not dangerous and even serve as food for smaller fish species. They can, however, clog the filtration system and even lead to ammonia spikes, with enough of them dying in the ecosystem.

The latter outcome is generally more prevalent in heavily infested environments with hundreds of bodies piling on the substrate. You have no business reaching that point, to begin with.

The situation is entirely different when discussing planaria and hydras, though. These organisms are predatory in nature, so you should limit or even eradicate them if possible. Their presence is more detrimental overall, despite providing some benefits along the way.

Fortunately, planaria worms and Hydras are not naturally-occurring in the aquarium and are most likely the result of outside contamination.

So, let’s get to that!

How to Prevent Tiny Bugs in Fish Tanks?

I would say there are 4 ideal approaches in this sense:

  1. Quarantine decorations and plants – You should always quarantine and sterilize anything that goes into the tank, no matter where you got it from. Live plants need sterilization which you can achieve via different means, including vinegar or bleach solutions (I’ve detailed these procedures in another article.) The same goes for rocks, driftwood, or any other aquatic element and piece of equipment that goes into the tank.
  2. Quarantine fish – This is an absolute must. Newcoming fish may carry parasites, bacteria, fungi, or any number of micro-hitchhikers that could infect the entire ecosystem. You never know what one fish might carry with it, which makes the quarantine procedure paramount for the ecosystem’s health and security. Prepare a quarantine tank and keep your fish there for at least 2 weeks before calling the green light.
  3. Keep the ecosystem clean – Frequent and thorough ecosystem cleaning and maintenance are key to preventing bug infestations. Remove algae manually, add in some algae eaters like snails and fish, vacuum the substrate to remove detritus, clean the filtration system, and perform regular water changes. You should always monitor the water’s quality and adopt a strict maintenance routine depending on the tank’s size and the type of aquatic animals you’re housing. A clean ecosystem is less likely to experience bug issues.
  4. Control the population – Sometimes, there’s little you can do to prevent some of the bugs, primarily copepods, but you can control their population. Keep the tank clean and add some copepod eaters into the tank, which should be fairly easy given that mostly all fish species eat them.

These measures should be enough to prevent, control, and even eradicate the tiny water bugs plaguing your aquarium.


As you can see, there are multiple types of microorganisms that thrive in aquatic ecosystems, some of which are more harmful than others. Learn about the differences between them and consider my prevention and control methods to keep them in check.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
Leave a Comment

Your email address will not be published. Required fields are marked *