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How To Prevent Fish From Getting Stuck To Filters – All You Need To Know

how many tetras in a 20-gallon tank

Wondering how to prevent your fish from getting stuck to the filter?

You can take advantage of what fellow aquarists have learned from their experiences with filter-related fatalities.

Preventative Measures

Here are some of the most popular preventive measures you can take.

Install a foam pre-filter

A pre-filter is basically a physical barrier between your fish and the filter’s water intake.

Sounds pretty handy, right?

This simple addition to your tank’s filtering system will protect fish fry, small fish, shrimp, and even long-finned fish from getting stuck to the filter. And if foam pre-filters can protect even the most vulnerable fish from getting stuck, it will work just fine for any type of fish.

This fine foam filter won’t lessen the strength of your filter, as the holes in the foam are large enough to not obstruct optimal water flow.

See why you need a pre-filter for your aquarium here:

Use filter sponges

A filter sponge works in a similar way to the foam pre-filter. The difference between these two filtering media is that the filter sponge is a lot coarser (with bigger holes) than the foam pre-filter.

This is a great add-on to your filtering system if you want to go longer without having to clean your pre-filter media.

You can remove and clean a filter sponge once every two weeks. A foam pre-filter could sometimes need to be cleaned two times a week.

Undergravel filtering systems

Undergravel filters are considered to be biological aquarium filters, working in a totally different way than mechanical filtering systems or chemical filters.

These filters are basically plastic plates that lay on the bottom of your tank. Each plate has lots of small holes in it and is covered by aquarium gravel.

Each corner of this undergravel plate will be equipped with a lift tube that connects the plate to the top of the tank. Water will get pushed up by an air-pump powered air stone or by a powerhead.

As the water gets drawn back through the gravel, it gets filtered efficiently without ever running the risk of a fish getting stuck to it.

To keep this filtration system working at an optimal level, you’ll need to thoroughly clean the gravel during water changes.

Alternative methods

If a new filtering system, or pre-filter foam (though very cheap!), is just not in your budget at the moment, and you’ve got a serious problem with fish getting stuck to your filter, there are two alternative measures you can take:

  • If your filter seems to be too strong for your aquarium, you can drill a hole or two into its intake tube. This will weaken the strength of your filter without a significant drop in its water filtering efficiency;
  • If you want to try out the “physical barrier” method of preventing fish from getting stuck to the filter, you can use dark-colored crafting plastic mesh to put around your filter’s intake tube. Hide it with some plants and check if it needs cleaning often.

How To Stop Fish From Getting Stuck BEHIND Filter

how to prevent fish from getting stuck behind filter

Getting sucked in by a filter’s intake is somewhat different from fish getting stuck behind a tank’s HOB (hang-on-back) filter.

Aside from using this spot as a refuge area, fish are drawn to hanging out behind the water filter for two reasons:

  • Instinctually knowing that the area where the current is the strongest is where food will be more readily available. And they’re not wrong; fish food will eventually end up near the filter, thanks to the constant flow.
  • Breathing in the water is easier for fish in the area of the tanks where the water is more oxygenated.

The best way to prevent fish from getting stuck behind a filter is to use cut-to-size pieces of foam pre-filters to fill in the gap between the filter and your tank’s walls.

How To Get Fish Out Of Filter (If They’re Already Stuck)

Firstly, unplug the filter and try to move the fish off of the filter as gently and carefully as possible. Damaged fins or scales can be just as deadly as staying stuck to a filter.

If the fish you rescued does end up getting injured during removal, consider transferring it to a quarantine tank to give it some time to heal without being harassed/bullied for being vulnerable.

Quarantining a fish that got stuck to the filter will also give you the opportunity to monitor whether or not it was diseased before getting caught in the filter’s intake. You can then prevent diseases/infections from spreading to the rest of your fish.

If the fish stuck to the filter is already dead, follow the same two steps (unplug filter & remove fish), and then discard it safely.

Kinds Of Fish That Might Get Stuck To Filter

Guppy

Coming home or waking up to a fish stuck to your tank’s filter is always a bit heartbreaking. It happens to novice fishkeepers and experts of the hobby alike.

The key to learning how to prevent fish from getting stuck to a filter is taking a pro-active approach. The more preventive measures you take, the fewer casualties you’ll end up with.

Healthy fish, large or small, will rarely get stuck in a filter. Their natural instincts take over, and self-preservation kicks in.

Some fish will manage to escape a filter’s intake if they’re not part of the “at-risk” categories of fish listed below:

  • Fish fry;

Fish fry are minuscule inhabitants of a tank, especially when compared to mature fish. Keeping them in a community tank will not only leave them defenseless against all the other larger fish in the tank but will also make them vulnerable to getting stuck to the filter.

  • Fish juveniles;

Just like fish fry, juveniles of most species can be overpowered by the intake of a medium-range aquarium filter. A quarantine tank for adolescent fish with an alternative filtering method will keep them safe until they’re strong enough to withstand the pull of a filter.

  • Small fish;

In general, small healthy fish can navigate around a filter’s intake and keep out of harm’s way.

However, fun-sized tiny fish can get stuck to a filter on occasion, simply by accident.

  • Clumsy swimmers;

Clumsy swimmers don’t necessarily belong to a species or other. Individuals of any genus can be more prone to getting themselves in trouble. However, others of its kind do just fine in the same tank conditions.

Not much you can do in this case except equipping your tank with a pre-filtering area.

  • Long-finned fish;

Fish with long flowy fins will not typically stay stuck if they get caught by a tank filter’s intake. But it takes just a few seconds of having a delicate fin stuck in the intake. This can cause some serious damage.

Fancy tailed goldfish (Carassius auratus) and Betta fish (Betta splendens) can have a hard time navigating the part of the tank where the filtering system is located.

  • Fish that explore tight hiding spots in general;

Fish species that love to explore and hide into the crevices of your aquarium’s décor, live rock, or driftwood pieces will also get too close to a tank’s filter and occasionally get stuck.

Guppy fish (Poecilia reticulata) are double-trouble in this sense. Guppies like to explore tight spaces, so the area behind a filter is too tempting for them to resist.  They can get their tails stuck in the filter’s intake and then not have the strength to set themselves free.

  • Dead or sick fish.

Before you start looking for causes or culprits when finding a fish stuck to the filter of your aquarium, consider the fact that the fish might have been sick without you noticing it.

And if you find new additions to your tank stuck to the filter the next morning, take into account that they might have died even before getting stuck due to the transfer itself.

Why Did My Fish Get Stuck In The Filter?

Hyphessobrycon amandae

Aside from the one-off casualties, there are a few reasons why fish can end up getting stuck to a tank filter.

The good news is that you can take precautionary measures in order to address the root of the problem in most of these cases.

Not cycling a tank before adding fish

Cycling a tank can trigger some sudden (and sometimes deadly!) spikes in the toxicity of your tank’s water. This trigger can be the culprit if there is more than one fatality in a short window of time.

Neglecting this step and introducing fish to an aquarium that is in the process of cycling can kill even the hardiest aquarium fish. And dead fish will, more often than not, end up getting stuck to the filter.

Finding fish in the tank filter’s intake without noticing them dropping off one by one beforehand is totally possible. A spike in ammonia levels will wipe out an entire tank in no time.

If you suspect this might be the reason why you’re finding fish stuck to the filter, start over by cycling your tank. Check your tank’s ammonia level if you’re unsure, and maybe schedule some water changes if your water parameters are off.

Why is cycling a tank so important?

In a cycled aquarium, beneficial bacteria have had time to grow and get established (mostly in your tank’s filter). Once you introduce the fish and their waste starts producing ammonia, the bacteria will convert it, first into nitrites and then nitrates.

Ammonia and nitrites are both toxic to fish. So, without the help of beneficial bacteria, the waste your fish create will end up killing most of your new additions to the tank.

If cycling a tank isn’t a feasible option, you can do partial water changes (at least 50%) often until bacteria get established in the new tank.

You can speed up the process of cycling a tank by adding a cupful of gravel from an already cycled tank. 

Not enough hiding spots

There are plenty of reasons why fish of all sizes might look for a hiding spot in a tank.

Being newly introduced, feeling overcrowded, and wanting some alone time from other co-inhabitants, or just instinctually taking cover when chased or harassed by other fish are all valid reasons why fish will hide in an aquarium.

This isn’t a problematic behavior, and it’s 100% natural for fish to hide.

What can be problematic is the lack of hiding spots in your tank’s setup.

You’re just setting yourself up for a lot of issues right off the bat if you don’t add stones, live rocks, aquatic plants, and décor elements with crevices to your tank.

Fish will find the biggest thing they can use as a cover, which happens to be your aquarium’s filter. Swimming close to the filter and trying to hide behind it will likely cause few fish to get stuck to a filter.

Water flow that’s too strong

The water flow inside your tank can be too strong for some fish. Or it could feel that way if your aquarium is too small for the filter you’ve chosen.

Some fish will hide behind a tank’s filter (and get stuck!) just because they want to get a break from the constant heavy water currents.

Small fish can also find themselves getting sucked into the water filter’s intake if the filter is too strong.

There are two ways you can fix this issue:

  • Work on your tank’s aquascaping setup, and include short bushy aquatic plants where the fish can seek refuge and rest when feeling overwhelmed by the tank’s water flow;
  • Change the size of your tank’s filter to match your aquarium’s dimensions.

Sick fish

Sick fish, and even pregnant females, will try to hide behind the tank’s filter. This is because they feel vulnerable and/ or because they are getting bullied by other fish.

Although they could muster up the strength to escape a filter’s intake when not sick/or pregnant, these fish will most likely get stuck to the filter just because of their close proximity and weak state.

In this case, a quarantine tank for sick fish might be useful. You can choose an alternative filtering system to prevent sick fish from getting stuck to the filter.

How Often Should You Clean The Filter

goldfish

Basic aquarium hygiene is vital to keeping your fish alive and healthy.

A tank’s maintenance routine should look something like this:

  • Periodic partial water changes;
  • Monitoring water parameters;
  • Tank, filter, and gravel/substrate cleaning.

A clean filtration system (and a clean filter intake) will keep your filter running efficiently.

If your filter’s water intake is dirty or obstructed, the way in which it sucks in water can change. That’s when accidents can happen.

Fish will get trapped much easier by a dirty filter than by a clean, optimally functioning one.

The general rule of thumb is that you should clean your tank’s filter once every four weeks.

Tip: Clean your filter using aquarium water instead of chlorinated tap water. This way, you’ll avoid damaging the established culture of bacteria in your tank.

Fish Tank Air Pump Vs. Filter

Aquarium air pumps and tank filters have some overlapping features, but they serve inherently different purposes. First and foremost, one of them is considered to be less essential than the other.

Quick aquarium air pump guide

An aquarium air pump’s sole purpose is to pump air. It is typically used along with plastic tubing, which connects the pump to an air stone. The end result: bubbles galore!

To safely use an air pump, you will also need a check valve and a regulator valve.

Air pumps don’t exactly add oxygen to a tank. But producing movement and agitation in the water increases water-air contact, which is vital to oxygenation in an aquarium environment.

Air stone bubblers can create a mesmerizing view in any tank. But they are considered to be mostly a decorative element.

Quick tank filter guide

Taking the typical HOB (hang-on-back) filter as a reference, tank water filters will clean the water. They can do this by drawing up water through an intake tube, pushing it through a filtering medium, and then releasing it back into the aquarium.

A filter will increase the water’s oxygen level in a tank by causing movement at the water’s surface. This is where the oxygen exchange between water and the atmosphere happens.

The constant movement of the water flow that a filter creates will also distribute oxygen evenly throughout the tank. This can keep fish and aquatic plants healthy at all levels of the tank.

Tank filters outrank air pumps in the fishkeeping world, as they serve more than one purpose. Filters are the breeding grounds of the vital bacteria needed to establish a cycled tank, and they clean and help oxygenate the water.

There are instances where water filters and air pumps can be used together. Undergravel filtering systems are a perfect example. 

Conclusion – How To Prevent Fish From Getting Stuck To Filter

Harlequin Rasbora, rasbora heteromorpha

You can certainly prevent fish from getting stuck to a filter.

The main takeaway here is that you should look at more than just “why” your fish got stuck.

Taking water parameters, tank conditions, filter strength, etc., into consideration can help you find the perfect preventive measure for your particular situation. 


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