White Fungus on Uneaten Fish Food – What to Do?

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

Fish require a healthy and fresh environment to remain healthy and happy over the years. Inadequate water conditions and a dirty environment will stress and affect them considerably, leading to health issues along the way.

This isn’t a vital issue if you already have a steady cleaning routine in place. However, you will begin to notice ominous signs if you don’t. One of them is the emergence of white fungus on uneaten fish food, substrate, and even on the fish.

So, let’s discuss about that!

What Causes White Fungus on Fish Food?

White fungus requires 2 primary environmental conditions: organic matter and humidity. These are widespread in any aquarium, especially those lacking proper maintenance and cleaning. Food residues will accumulate on the substrate, infiltrate the bed, and begin to decay out of sight. They will produce ammonia and nitrites and can overwhelm the filtration system and the tank’s natural colonies of nitrifying bacteria.

This will cause ammonia spikes which can kill your fish. Another direct repercussion is the appearance of white fungus, which is actually a type of mold. And you don’t want that for all the reasons which we will discuss shortly.

Is White Fungus Harmful to Fish?

White fungus doesn’t affect the health of your tank inhabitants directly, but it will do so indirectly. The problem is that the white fungus will further decrease water quality, causing more bacterial overgrowth and even the emergence of other types of fungi and mold infections.

One of these outbreaks will eventually affect the fish directly, causing respiratory problems and infecting their kills, skin, or digestive systems.

But, above everything else, the presence of white fungus is a sign of deteriorating aquatic conditions. This alone should be enough of a drive to mobilize you into tackling the problem asap.

Getting Rid of Spoiled Food in Your Tank

The best way to remove white fungus is by eliminating its trigger – spoiled food. This achieves 2 things: eliminates any fungi or mold that may feed on the food and eliminates the source of ammonia. When dealing with this problem, consider the following 3 solutions:

– Vacuum the Substrate

This is the first line of attack because vacuuming the substrate will instantly eliminate all food residues, fish waste, and other dead organic matter. The process shouldn’t last more than a couple of minutes, depending on how large the tank is and the overall layout.

When vacuuming the substrate, remember to:

  • Be thorough about it and go over the same areas several times for the best results
  • Don’t disturb the plants and fish in the process
  • Don’t tip over tank decorations, and don’t disturb the overall setup
  • Be careful not to take in any of your bottom feeders in the process

Ideally, you should vacuum the substrate regularly, but not too often. Your fish may become stressed in the process. We’ll discuss how you can circumvent this problem in the following sections.

– Regular Water Changes

As a fish keeper, I realize that water changes can sometimes become a drag. Especially since some fish require more frequent water changes than others. But there’s no denying that water changes are essential for keeping the environment clean and well-oxygenated.

Weekly partial water changes will contribute to a healthier environment by:

  • Diluting excess nitrates and keeping ammonia and nitrites to 0
  • Improving oxygenation in the water
  • Removing floating particles that muddy the water, including excess fish waste, food leftovers, or dead plant matter

As a general rule, you should perform at least one water change every week and only change up to 15% of the total water volume in one session. You don’t want to go over that unless it’s absolutely necessary for some reason. Massive water change will dilute the minerals in the water, which isn’t ideal.

Also, the smaller the tank is, the more frequent the water changes. Larger environments are generally more self-sustainable. At the same time, some fish species demand more frequent water changes due to being messier eaters and poopers. Goldfish and African cichlids fall into this category. Just a heads-up so you know what to expect if you don’t already own these fish.

– Have Reliable Filtration

It’s true that not all aquariums demand a filter. But it’s also true that the filter makes the fish’s life (and yours) a lot better and easier. Having a reliable filtration system in place to keep the water clean and well oxygenated and your tank maintenance schedule will be much more forgiving.

The filter will oxygenate the water and remove floating particles like food residues before reaching the substrate. The filter will reduce the need for frequent tank cleaning because it will keep the water cleaner for longer.

How to Avoid White Fungus in Your Tank?

So, are there ways to avoid white fungus in your tank? Sure, there are. Consider the following:

– Smaller Food Portions

Fish have a tendency to eat more than they’re supposed to. This leads to a lot of food residues sinking to the tank bed, and that’s where all your problems begin. The solution is simple: just feed your fish smaller portions. Fish don’t need too much food, to begin with; the ideal meal size should allow the fish to consume it within 2-3 minutes at most.

Everything else above than that turns in residues.

Always feed your fish smaller portions more often than one big meal per day. This prevents digestive issues and keeps the fish’s habitat cleaner in the long run.

– Choose the Right Substrate

Some substrates are easier to clean and maintain than others. Sand comes to mind. Sand is very compact, so food residues, fish waste, and general dirt will remain on the surface, allowing you to spot and clean them easier. The vacuuming is a bit trickier with sand, though, because sand particles will flood the entire water column in the process.

You also risk disturbing the anaerobic pockets that contain concentrated ammonia and can foul the water. Fortunately, you can prevent ammonia pockets by having a good maintenance schedule in place.

If sand isn’t to your liking, gravel is another good option. Gravel is easy to clean and arrives in different sizes, each type with its own benefits. If the particles are large enough, you can vacuum the substrate easily. If they’re small, the food residues will remain on top, just like with sand.

You can also go for a bare-bottom tank if your fish don’t mind. The benefit is that this makes waste visible and easier to remove.

– Preventive Cleaning

This is the most important point on today’s prevention list. Nothing beats preventive cleaning when it comes to keeping the environment healthy and clear. Vacuum the substrate regularly, remove visible dirt when present, and do partial water changes weekly. A good maintenance schedule is the best approach when looking to prevent fungi, mold, or algae invasions.

What Fish Will Eat White Fungus?

Interestingly enough, some fish species consume white fungus, algae, and dead organic matter, keeping your tank cleaner in the long run. These include plecos, the Siamese algae eater, several catfish species like twig and otocinclus, mollies, etc. I think that cleaner fish should be present in any aquatic setup.

They consume residues produced and ignored by other fish, contributing to the system’s overall chemical and biological stability. That being said, don’t think that cleaner fish can replace your tank maintenance routine. You still need to clean the aquarium regularly anyway.

The difference is that you most likely won’t need to do it as often.


White fungus can become a problem in any aquatic setting. Fortunately, it’s quite easy to keep it away by resorting to any of the preventive methods I’ve suggested.

Also, don’t forget, regular cleaning and maintenance keep the environment more stable and improve your fish’s lifespan and quality of life. Don’t skip aquarium maintenance day!

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 *