8 Reasons Your Corydoras Are Glass Surfing!

Corydoras start glass surfing for various reasons, including spawning, water quality, tank size, new environments, insufficient schooling size, hunger, boredom, and reflections in the aquarium.

My corydoras began glass surfing within a week of being added to my aquarium, after researching the potential causes, I decided to publish my findings here.

What Is Glass Surfing?

Corydoras Glass Surfing
Corydoras Glass Surfing

“Glass surfing” refers to a behavior in which fish swim along the aquarium glass for extended periods each day. Fish may swim horizontally or vertically across the glass, appearing to “surf” it, making the behavior quite noticeable.

Many people worry that their fish are glass surfing due to a problem in the tank, but there are several normal, natural reasons why your corydoras might exhibit this behavior.

Why Do Corydoras Start Glass Surfing?

One Of My Corydoras
One Of My Corydoras

Here are the most common reasons corydoras glass surf:

  • Spawning
  • Water Quality Issues
  • Small Tank
  • New Environment
  • Insufficient Schooling Size
  • Hunger
  • Reflections
  • Boredom

Depending on your aquarium, you may be dealing with multiple issues simultaneously.

Below is a breakdown of each problem to help you identify why your corydoras are glass surfing and address any potential issues in your tank.

Spawning

Corydoras Eggs In My Tank
Corydoras Eggs In My Tank

Female corydoras may glass surf before spawning as they search for an appropriate spot to lay their eggs.

Fortunately, it appears this was the reason my corydoras started glass surfing in my tank. The photograph above shows one of the many egg clutches I found in my aquarium.

Corydoras will rapidly swim over the glass surfaces, usually moving left to right horizontally, to find a suitable place to spawn. This behavior is normal and not a cause for concern, but it can be difficult to confirm until you see the eggs in your tank.

Corydoras eggs are small, white, and sticky, making them easy to spot on the aquarium glass. It may take a week or so for the eggs to appear after the glass surfing behavior begins.

Water Quality Issues

Testing Water Parameters
Testing Water Parameters

Corydoras may start glass surfing if there are issues with the water parameters in their tank.

While many people immediately focus on ammonia, nitrite, and nitrate levels, it’s also important to check other key water parameters such as temperature, pH, and chlorine levels.

Problems with any of these parameters can stress your corydoras, leading to glass surfing until the issue is resolved. Think of glass surfing as your corydoras’ attempt to escape low-quality water and find water with suitable parameters.

I prefer using the API Master Test Kit to check my water parameters because it is easy to use and much more accurate than test strips. However, the kit doesn’t test for chlorine, so it might be a good idea to use some inexpensive aquarium test strips specifically to check chlorine levels if you use tap water for your water changes.

Below is a table of the recommended water parameters for Corydoras aeneus, which are similar to those for many other cory species.

Water Temperature68 to 82 °F (20 to 28 °C)
Water FlowStill-Moderate
pH6.0–8.0
GH2–30 dGH
KH2-15 dKH
Ammonia0 ppm
Nitrite0 ppm
Nitrate<10 ppm
Corydoras Aeneus Water Parameters

Small Tank

My Community Tank
My Community Tank

Corydoras may start glass surfing if they are kept in a tank that is too small for them.

I keep my albino Corydoras aeneus in a 29-gallon community tank to ensure they have plenty of space to forage on the substrate.

Different types of corydoras grow to various maximum sizes and require different tank sizes to feel comfortable. Additionally, the footprint of the tank matters significantly because corydoras spend a lot of time on the substrate.

Tank Size

For example, a 29-gallon long tank may have a 30 x 15 inch (76 x 37 cm) footprint, while a 29-gallon cube tank may have an 18 x 18 inch (45 x 45 cm) footprint.

The long tank offers much more substrate space for your corydoras to forage on compared to the cube tank, even though both are 29 gallons in size.

Corydoras Species

I keep Corydoras aeneus in my community tank, which can grow up to around 3 inches (7.5 cm) in length. In contrast, Corydoras pygmaeus only reaches about 1.2 inches (3 cm).

A fully grown Corydoras aeneus is more than twice the size of a Corydoras pygmaeus, requiring a larger tank to meet its needs.

This issue is often not the fault of the fish keeper, as much online advice treats corydoras as a generic species with the same requirements, which is not accurate.

You may be able to keep a smaller species like Corydoras pygmaeus in a small tank without it glass surfing, but a larger species like Corydoras aeneus may have problems in that same tank due to insufficient space.

Matching Tank Size To Corydoras Type

AqAdvisor Stocking Calculator
AqAdvisor Stocking Calculator

I like to use the stocking calculator on AqAdvisor.com to get a rough idea of how many corydoras I can keep in my tank.

It is quick and easy to use, allowing you to select the specific type of corydoras you want to keep and enter the exact dimensions of your tank.

While AqAdvisor isn’t perfect and has some flaws, it is a useful tool that can help prevent your corydoras from glass surfing due to being kept in a tank that is too small for them.

New Environment

My Community Tank
My Community Tank

It is normal for corydoras to glass surf in a new tank as they acclimate to their new environment.

This behavior can last up to a month, but most corydoras will settle down after a week or two.

If your corydoras are still glass surfing after being in the tank for more than a month, there are likely other issues causing this behavior.

Insufficient Schooling Size

3 Corydoras And 2 Honey Gourami
3 Corydoras And 2 Honey Gourami

Corydoras are social fish that thrive in the company of their own kind, with most recommendations suggesting a minimum of six corydoras per tank.

That said, I have kept groups of three and give corydoras without issue.

In my experience, aside from glass surfing while spawning, my corydoras seem content and spend most of their day foraging for food.

However, if you have only one corydoras in your tank, it might be glass surfing due to the stress of being alone.

Adding other fish or even different species of corydoras may not be sufficient to alleviate this stress, as most corydoras need companions of the same species to feel secure.

Hunger

Bug Bites Bottom Feeder Formula
Bug Bites Bottom Feeder Formula

Some corydoras may start glass surfing due to a lack of food in their tank, a problem more common than people realize.

Many beginners mistakenly believe that corydoras will eat the algae in their tank, but this is rarely the case. While some corydoras may consume a small amount of algae, it is not their primary food source.

Another common mistake is assuming that leftover food falling to the substrate will be sufficient for corydoras. This is not accurate, as they need to be specifically fed to ensure they receive adequate nutrition.

It’s important to target feed your corydoras to make sure they are getting enough to eat. My corydoras love Fluval Bug Bites, and I highly recommend them to anyone keeping corydoras.

I target feed my corydoras twice a day, and they also eat any leftover food that sinks to the substrate, helping to keep them happy and well-fed.

Boredom

A Foraging Corydoras
A Foraging Corydoras

Fish can get bored and engage in random behaviors to entertain themselves, a phenomenon more common than most people realize.

For example, one of my corydoras often appears bored, lies on the substrate for a few seconds, then aligns itself toward my neon tetras and swims through the middle of them as fast as it can.

I’ve observed this behavior countless times and can’t explain it other than the corydoras simply being bored.

Similarly, your corydoras might be glass surfing out of boredom and a desire to burn off some energy.

Reflections

Although I haven’t observed it in my own tanks, several people have reported that their corydoras seem to glass surf against reflective surfaces.

These individuals speculate that their corydoras might be trying to reach their reflection, mistaking it for another fish.

While I haven’t seen this behavior in my own tank, it should be easy to check if your corydoras is consistently swimming against a reflective surface in your aquarium.

Final Thoughts

Glass surfing in corydoras can be attributed to several common causes ranging from spawning behavior to external tank conditions such as water quality, insufficient tank size, or even reflections.

Understanding these triggers is essential for fish enthusiasts to provide an optimal environment for their beloved pets.

By recognizing and addressing these potential issues, one can ensure the well-being and health of corydoras, promoting their natural and stress-free behaviors in the aquarium.