When fish rub their body against the substrates of the fish tank, this is technically known as flashing. There can be many reasons for you to find your cichlids rubbing on sand or scratching on rocks; Poor water quality (such as the presence of ammonia, nitrates, hard water, increased temperature and pH) and infectious diseases like ich are top culprits that make your cichlids rub their body on sand or scratch on rocks, trying to get relief using the tank’s substrate.
There are other reasons, too, which we’ll explore – Plus ways to make it stop and to help your cichlids from the discomfort they’re experiencing.
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2. What is Flashing?
Flashing refers to the behavior of fish rubbing on sand, scratching on rocks, or otherwise rubbing against items in the tank (though it’s usually substrate). It’s most commonly used to scratch an itch (though not always – more on that in the next section).
Like humans, they want to scratch that annoying itch. Unlike humans, they don’t have arms or hands, so they have to rely on their surroundings to try to get relief. This itch is frequently a result of parasitic infections.
That said, there are other things that can cause fish to flash, which we’ll dive into next.
3. Why Do Cichlids Flash?
Okay, this is actually a pretty big topic, but I’ll do my best to condense it here. Some are more common than others, so I’ll start with the most common.
There are LOTS of reasons why your cichlids might be flashing, but the most common one is parasites (specifically, gill or body flukes), ich, and velvet.
Think of it this way: When your fish is rubbing against the substrate, they’re itching and uncomfortable. That irritation makes them scratch against whatever they can to get relief: Plants, sand, gravel, etc. You may also observe your fish twitching or swimming a little differently, reflecting their discomfort. They may have increased stress and/or changing body color as accompanying symptoms.
While these are common reasons, they’re compounded by the fact that to an extent, studies show that some flashing might be just normal business as usual for some cichlids (mbuna, I’m looking at you!) We’ll talk about why that is, and how to tell the difference.
I strongly recommend working your way down the list below to determine the root cause, because you’ll definitely want to be able to rule out things that could be detrimental to your cichlids’ health.
4. Why are My Cichlids Rubbing Against Sand or Rocks?
This behavior is known as flashing. Your cichlids are rubbing against sand or rocks because they’re either itching, laying eggs, sick, showing dominance, or stressed somehow. These are all reasons a cichlid may flash, and it takes a sleuth-like process of elimination to determine which one it is.
Rule out the reasons with the most negative potential first, like ich and parasites. In fact, it’s not a bad idea to take a combination approach and do a preventative salt treatment just to be safe.
Also, ask yourself: Is only one cichlid flashing? Or all the cichlids in your tank? Is it only the cichlids, or is the algae-eater going at it too? Did it start with one fish before you started seeing it in others? Or is it always the same two fish flashing? These questions will be key to help you understand what’s going on.
Remember to move affected fish to a quarantine tank when possible, to prevent any diseases from spreading.
Ich is a parasitic disease that appears as tiny white spots on the body of the fish. This indicates newly infected plants or tank mates. Ich can cause your fish pain by creating breathing issues, skin infections and imbalanced swimming. It can also be the cause of your cichlid flashing or twitching in the aquarium water.
Common solutions for treating ich include salt treatment (1tbsp per 2 gallons) with partial water changes to get rid of the parasite, anti-infection medication, and upping the temperature to kill the parasite. Depending on what fish you have in your tank, you may also be able to use Mardel’s Coppersafe, which has the benefit of also treating other potential culprits for flashing, such as gill flukes and velvet – Which we’ll discuss next.
NOTE: Don’t use Coppersafe if you have invertebrates, as it’s harmful to them. Also check to make sure your fish species aren’t sensitive to copper before using it.
Golfish with ich, removed from main tank.
Similar to ich, velvet is another parasitic disease that has plagued aquarists since the hobby began. It’s similar to ich as it affects the body of the fish, leaving tiny, blister-like particles on the skin. It gets its name because this disease creates a velvet-like structure on the body of the fish.
Velvet causes itching and flashing, which could be the reason your cichlids are rubbing on sand and scratching on rocks. It can be hard to see at first, but one way to examine for it is to turn off all the lights and then inspect your fish with a halogen-bulbed flashlight. Look for a rust or white-colored coating.
Some treatment methods that are also used for ich may help treat velvet (such as increasing the temperature), but a tried and true go-to method is Coppersafe by Mardel for 10 day to 2 weeks. Just be VERY careful to remove invertebrates and plants before use, as it’s toxic to them – And check to make sure you don’t have any fish species that are sensitive to it. You can also just opt to treat fish in a quarantine tank instead.
It’s not always diseases or water issues that cause cichlids to be rubbing against sand or rocks. Depending on the species, when some cichlids are ready to lay eggs, they’ll start cleaning “their” rocks by rubbing their body, face, or lips on them.
4.4 Poor Water Quality
As an aquarist, you know that water quality has a huge role in the health of your fish. Poor or sub-par water quality causes ammonia, which can cause your cichlids to flash. Poor water quality and/or increased ammonia levels stress and can damage the gills, skin and organs of your fish and as result, they rub themselves against various surfaces to try to get relief.
Similarly, increased water pH, chlorine, low mineral levels and nutrients, along with dangerous bacteria or extra fungus can also create infectious issues for the cichlids, causing them to start rubbing their skin/body against the sand and rock.
Test your water quality and parameters, clean your tank, and perform partial water changes until the quality is back up to par. Note that if your tank is extremely dirty, you should do water changes even more gradually than usual, so as to prevent shocking the fish with the change in chemistry.
This one may be a little obvious, but it’s still worth saying. Stress can cause behavioral changes, and flashing and twitching may be an expression of that.
Stress could be caused by an increase in the ammonia level or other chemicals, an overcrowded tank, incompatible tank mates or fin nippers, unstable water parameters, poor maintenance, and on and on.
4.6 Boredom or Attention?
I’m a little on the fence about including this one, but I do think it’s possible. I haven’t seen it, but I’ve read MANY accounts of cichlid owners on forums who insist that their cichlids will flash to get their attention.
It’s just not well-studied, but it’s possible. With limited means of expression, cichlids may rub on sand and scratch on rocks as a way of showing they want food, attention, or are bored. I would only land here if you have pristine water quality, have already treated for ich/velvet/flukes, done all the testing and quarantining, etc. etc. And even then, I think the next reason is much more likely, especially for cichlids…
4.7 Territorial Display
Remember how I said at the very beginning that all of these potential reasons are complicated by the fact that to a degree, a bit of flashing might be just normal for some cichlids? Well, a 2011 Rutgers University study found that when two male mbuna cichlids were placed together in a single territory, they began to fight over it by making dominance displays. Those displays included making their fins look bigger, changing their colors, biting and ramming, and guess what else? Flashing.
While this study was conducted with mbuna cichlids, it’s not a far off possibility that other cichlids may do this too – Especially considering that there are related anecdotal accounts from cichlid owners. Cichlids are a territorial fish, so this tracks.
4.8 Gill Flukes
Gill flukes are a parasite occurring on the outside of the body, a group of nasty little flatworms called Platyhelminths. You can’t see them with the naked eye, but the fish may develop little red dots (called blood spots) that indicate flukes.
Gill flukes can cause secondary infections and should be treated with an antifungal and/or antibacterial med, or anthelmintics (Praziquantel). Because the flukes are attached to the gills, the fish may gasp for air at the surface.
It’s really hard to tell the difference between ich, velvet, and gill flukes, because the symptoms can be very similar, and you may not even be able to know for sure unless you put the fish under a microscope (which isn’t really possible). To mitigate this, aquarists may just treat for all three.
I strongly recommend reading this guide on gill flukes.
4.9 Physical Injuries
The presence of fin nippers or aggressive tank mates can result in physical injuries to your fish. When being chased by a more aggressive fish, they may injure themselves on decor, substrate, rocks, etc. Cichlids are aggressive, and may even bite each other. These physical injuries can cause your cichlids to flash in discomfort.
5. What to Do If Cichlids Are Rubbing on Sand/Rocks?
What you do depends in part on what’s causing your cichlids to flash. I would start with water quality and testing, and performing partial changes. Quarantine affected fish for treatment. It’s worth treating for ich/velvet/flukes as the same treatment(s) can knock out all three.
If you’re treating the whole tank, you’ll need to make sure other inhabitants (including plants) are compatible with the treatments. If not, move them to another tank, and address cleaning/treating them there as needed. Invertebrates (including snails) should be removed before using Coppersafe, as it can hurt them.
Remember that just because everything looks fine doesn’t mean that’s necessarily the case. Water chemistry changes and some parasites can be invisible.
Quarantining new tank inhabitants, maintaining good water quality, avoiding overcrowding, and controlling ammonia and nitrates/nitrites in the tank is super important to help prevent diseases and stress.
If there is one cichlid in the tank who simply flashes from time to time, but there are no other symptoms, and no other fish in the same tank do it, then it’s possible it could be a dominance display. Ask yourself if the fish has always done this, or if it’s a new behavior, to try to narrow it down.
6. Cichlids Rubbing on Sand: FAQs:
6.1 Why is My Fish Rubbing on the Sand? Why is My Fish Rubbing Itself on the Gravel?
If your fish is rubbing its body on the sand (flashing), then it’s very possible that it could be suffering from infectious diseases and/or parasites, or the water quality is poor. If it’s a cichld, it could be normal behavior in some contexts. Eliminate the other negative possible causes first.
6.2 Why is My Fish Twitching?
Twitching is a symptom similar to flashing, and they’re often seen together. Many of the same things that cause flashing can cause twitching (poor water quality, parasites, injury, etc.) Work your way through the list in this article to rule out possible causes. Note that while the Rutgers study on mbuna cichlids showed flashing as a part of some dominance displays, it did not include twitching (thus potentially being more indicative of disease).