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Tetra Whisper In-Tank Filter 40i with BioScrubber - 20-40 gallon (25818), Black

4.3 4.3 out of 5 stars 19,758 ratings
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Amazon's Choice in Aquarium Filters by Tetra

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Up to 40-Gallons

Purchase options and add-ons

  • UNIVERSAL DESIGN: Tetra Whisper 40i Internal Filter is an all-in-one air pump and water filter system.
  • INTERNAL FILTER: Mounts on the inside of your aquarium with clip (included).
  • CATCHES DEBRIS: Dense, dual-sided mesh filters debris and fish waste.
  • AERATES WATER: Air-driven design filters up to 170 GPH while oxygenating water.
  • CONVENIENT DESIGN: Uses large easy to change Bio-Bag cartridges; filter mounts inside aquarium, making it possible to place tank flush against the wall.

Customer ratings by feature

Easy to clean
4.1 4.1
Noise level
4.0 4.0
Suction power
3.9 3.9
Sheerness
3.9 3.9

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Tetra Whisper In-Tank Filter 40i with BioScrubber - 20-40 gallon (25818), Black
Tetra Whisper In-Tank Filter 40i with BioScrubber - 20-40 gallon (25818), Black
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Price$14.90-38% $5.99
List:$9.59
$8.99-5% $39.99
List:$41.99
$17.99$16.99
Delivery
Get it as soon as Sunday, Mar 24
Get it as soon as Sunday, Mar 24
Get it as soon as Sunday, Mar 24
Get it as soon as Sunday, Mar 24
Get it as soon as Sunday, Mar 24
Get it as soon as Sunday, Mar 24
Customer Ratings
Easy to clean
4.1
4.3
4.0
4.5
3.7
Noise level
4.0
3.6
4.4
4.0
3.6
Suction power
3.9
3.7
3.8
4.2
3.3
Value for money
4.5
3.7
4.3
3.6
Sheerness
3.9
4.6
2.9
Sold By
Amazon.com
Amazon.com
MoonOrange
Fairyna
PUEUTU
JackSupermall

From the manufacturer

About Us

Tetra’s tradition of innovation started more than 50 years ago in Melle, Germany, where Dr. Ulrich Baensch founded the company (Tetra Werke) and pioneered the development of flake fish food - an innovation that revolutionized the industry. At the time, growing and harvesting food for your fish was a painstaking process. The advent of flake fish food not only made feeding your pet much easier. It opened the way for more people to own an aquarium. At Tetra, we’re dedicated to helping seasoned hobbyists and beginners alike enjoy a successful, life-long aquatic experience.

Product guides and documents

Product details

  • Is Discontinued By Manufacturer ‏ : ‎ No
  • Product Dimensions ‏ : ‎ 5.13 x 5.88 x 10.5 inches; 1.5 Pounds
  • Item model number ‏ : ‎ 25818
  • Department ‏ : ‎ Unisex-Adult
  • Date First Available ‏ : ‎ June 9, 2004
  • Manufacturer ‏ : ‎ Tetra
  • ASIN ‏ : ‎ B0002DHYH2
  • Country of Origin ‏ : ‎ China
  • Customer Reviews:
    4.3 4.3 out of 5 stars 19,758 ratings

Looking for specific info?

Product Description

The Tetra Whisper 40i Internal Filter for aquariums is the ultimate in quiet, convenient 3-stage filtration. This submersible filter mounts on the inside of the aquarium, rather than hanging from the outside, making it possible to place the tank flush against a wall and easily hide with tank décor. The air pump (included) provides bubbles that move water through the filter, efficiently filtering and oxygenating your aquarium. The water flows through Ultra-Activated carbon, absorbing odors and discoloration, as well as through the dual-sided mesh of the Bio-Bag Filter, trapping debris and fish waste. Filters up to 170 GPH while oxygenating water. The Tetra Whisper 40i Internal Filter adjusts easily to high or low water levels with a mounting clip. Each unit includes the filter, air pump, 2 feet of airline tubing and one large Tetra Whisper Bio-Bag Filter cartridge (change monthly – replacement small filter cartridges available). For 20-40 gallon tanks. Since 1951, Tetra has developed the world’s most comprehensive body of fish food knowledge, and fishkeeping enthusiasts have looked to the brand for products and solutions that add ease and beauty to their home. Whether you're an experienced hobbyist or just starting out, Tetra has everything you need – from a large variety of quality fish food and innovative equipment to test kits and decor.

Important information

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Customer reviews

4.3 out of 5 stars
4.3 out of 5
19,758 global ratings

Customers say

Customers like the ease of cleaning the filter, saying it really clears the tank up nicely. They also like the noise. However, some customers have reported issues with the sturdiness of the filter. They say it breaks after a few months and the rubber pieces are not holding up. Customers disagree on performance, size, filter, leakage, and value.

AI-generated from the text of customer reviews

899 customers mention637 positive262 negative

Customers like the noise level of the pet supplies. For example, they mention it's extremely quiet and the sound is a non-issue.

"...I use this in both of my betta fish tanks with no issues at all. Extremely quiet, especially considering one fish tank is right next to my bed on..." Read more

"...Sound is simply a non-issue. The guppies reproduce rapidly and their small fry have been safe. None have been drawn in by the filter's intake...." Read more

"...All four of them are not quite silent, but very quiet. There is a soft, low hum from the motor windings, a little bit like a transformer humming...." Read more

"...I love them.They are both very quiet. Aside from the sound of the water falling back in.. I mean it sounds like a waterfall...." Read more

499 customers mention404 positive95 negative

Customers like the ease of cleaning with the filter. They say it doesn't bother their betta and keeps the tank clean. Some say that it really clears the tank up nicely overnight, leaving the tank looking pristine. The filters are cheap and can be reused by washing with water.

"...I got the 10-30 filter, and it keeps my 40-gal tank clean. I clean it every1-2 weeks...." Read more

"Turtles create huge messes and this filter does an amazing job of keeping the water clean." Read more

"...filter size, my water now almost filled to the top, stays absolutely clean...." Read more

"...-They are both still easy to clean-They circulate water nicely at the surface..." Read more

935 customers mention637 positive298 negative

Customers are mixed about the performance of the filter. Some mention that it works pretty good, while others say that it never worked very well. The hook does not work with tank lids and the suction cups are weak.

"...And the results are as good as any other filter I've ever used, regardless of cost...." Read more

"...The 10i works perfectly in a 3 gallon tank, which I have two of and I have a 10i filter in each...." Read more

"...My 20i still works but my 40i just stopped working after only three months of use. That's terrible! It works really well when it's not broken though...." Read more

"It works great I just wish it had an adjustable flow rate" Read more

499 customers mention343 positive156 negative

Customers are mixed about the filter. Some mention that it is amazing, heavy, and good for any aquatic life. However, others say that it does not filter as well as the whisper. Some customers also mention that the filter always looked unused, and that it stops the filter from working properly.

"Filter works great. Had to replace the previous filter I had that was also a Tetra Whisper filter, my fault it broke down. It does have some noise...." Read more

"...out my filter for the 'recommended' filter size, as these filters work so good. I love them.They are both very quiet...." Read more

"...(unless you buy the model intended for reptiles), so the filter pads just sit there exposed...." Read more

"...It’s a good filter for a small tank just be ware of this!..." Read more

419 customers mention276 positive143 negative

Customers are mixed about the value of the filter. Some mention that it's easy and peace of mind, the cost of this filter is worth buying for any tank, and it'd be a waste of money. Others say that it feels and looks cheaper, has a weak design, and is clumsy. Overall, the opinions are mixed, and the filter is not perfect and may not be the best option for your pet's tank.

"...better than the filter cartridges for Marineland products and cost much less to buy...." Read more

"...Pros: Small.Cons: Bit expensive compared to the other sizes, loud, no suction cups (you have to clip it to the rim of your aquarium)..." Read more

"Price was most reasonable. I even ordered a second filter." Read more

"...the market for a new pump/filter...especially with how inexpensive the bulk filters cost. 12 filters for something like $8/year?! That's a steal." Read more

310 customers mention149 positive161 negative

Customers are mixed about the size of the filter. Some mention that it was perfect for their 5 gallon tank, allowed them to save space, and has a good pump for the size. However, others say that it's a little too big for their tank and takes up a lot of tank space.

"...10i Model - This filter is perfect for three gallon freshwater fish tanks. I use this in both of my betta fish tanks with no issues at all...." Read more

"...Another issue some people may have is that the cable may be a little too short...." Read more

"...The standard tank top fits nicely without interference with the filter...." Read more

"...It does barely fit in a ten gallon aquarium and it does use a tad more real estate than I'd like it to BUT it is rated 10-20 gallons so my use case..." Read more

266 customers mention148 positive118 negative

Customers are mixed about the leakage of the pet supplies. Some mention that the water has never been so clear, the filter itself is quiet and gets the job done with minimal water disturbance, while others say that it backflowed and leaked, overflows the filter cartridge, and drained their one tank. Some customers also mention that there is quite a bit of unused empty space.

"...is that it sits completely inside the tank so there is no possibility of water leaking onto the floor so long as it's positioned below the top of..." Read more

"...When the filter pad becomes clogged, it WILL overflow, but into the tank, not out of it...." Read more

"Runs quiet and keeps water clear." Read more

"...One thing I'll say is there is quite a bit of unused empty space...." Read more

278 customers mention74 positive204 negative

Customers are dissatisfied with the sturdiness of the pet supplies. They say that it breaks after 3 months routinely, the unit is pretty flimsy, and is too weak for a 10 gallon. Some complain that the top lid cover is floppy and the disposable filter is supposed to last a month. However, some customers say that the case does not come apart and the box ripped open.

"...The 40i is also a bit flimsy as the handle can come loose as the snaps that hold it in place can fail, and so a little superglue can be helpful...." Read more

"...A TOTAL PAIN to clean- heavy and awful to take apart, and something broke and when the power went out, it backflowed and leaked...." Read more

"...On a benefit/cost basis, these filters look really good. They are made of a tough, slightly flexible plastic, so even if you drop one on the floor,..." Read more

"...The accessory to latch it to the side of the tank is very flimsy and does not hold it up very well...." Read more

How can something so simple work so well?
5 Stars
How can something so simple work so well?
When you open the box, the Whisper 40i (or it's smaller siblings) don't seem very impressive. It's not much more than a oval plastic bucket, with another bucket (containing a motor and pump) snapped onto the bottom. If you looked at one and thought "this can't possibly work", you would be so wrong.Perhaps they work as well as they do BECAUSE they are so simple, and so have little chance for things to break. The pump sits IN your aquarium water, so it never needs to be primed. You plug it in, and it begins working, filling the upper bucket, where the water flows through the filter pad and spills back into the aquarium. No priming necessary ever, including after a power failure. When the power comes back on, it just starts working again. It's a shame that every hang-on-the back power filter can't make a similar claim, some unfortunately will lose their prime and/or fail to restart, resulting in unhappy fish and sometimes a damaged filter.There are no adjustments for flow, so these only run at one flow rate. Inevitably, some food can get sucked up if you let it run while feeding. I have the filters on a separate power strip, so when I feed my fish, I just use the switch on the power strip to turn the filters off for an hour or so. Easy solution and prevents the filter pads from clogging so quickly.There is no top or lid (unless you buy the model intended for reptiles), so the filter pads just sit there exposed. This means that the water in the filter is fully aerated as it passes through the pads. It also means that no other internal filter is as easy to change pads when they become clogged. The top edge of the pad is above the water line, so you just grab it with two fingers and lift it out. You don't have to disturb the suction cups or hanging bracket at all. You don't have to put your whole arm down into the tank. Maintenance which is easily performed is more likely to be done when needed, so easily changed pads are more likely to be changed when clogged.You have options for how you want to attach the filter. The box includes two suction cups, and a newly designed bracket which hangs over the edge of your tank. I use the bracket, as it's adjustable for height and I don't have to worry about suction cups losing their suction.The filter pads are the Whisper bio-bags, which amount to a thick fluffy poly bag, over a plastic frame, with carbon granules inside. Replacing these is simple, and if purchased in a 12 pack from Amazon, cost about 60 cents per bag.I used Emperor filters for years, and in my experience, these bio-bags work a lot better than the filter cartridges for Marineland products and cost much less to buy. If you rinse them under tap water, which is easily done, the cost is even less. Rinsing the bags doesn't disturb your biological bacteria since they are on a separate part (resembling a hair brush) which remains in the filter when you remove the bags.You do have some flexibility with regard to media options as well. You don't have to use the carbon which is included with the new pads. You can put anything you want inside the bag, and if desired, transfer it to the new bag next time you change them out. You also don't have to use the separate biological "hairbrush", and if you leave it out, you have room to put another media bag in it's place, with ceramic rings, or whatever else you can think of.I have four of these, mounted on two separate tanks, one 55 gallons, the other 75 gallons. All four of them are not quite silent, but very quiet. There is a soft, low hum from the motor windings, a little bit like a transformer humming. At first there was also a faint sound like air trapped somewhere, perhaps cavitation in the pump? But these sounds are hard to hear, and not distracting. And the cavitation sound went away on it's own after a few days. I can hear the soft humming sound if the room is totally quiet and I stand near the tank, but if there is any significant sound from conversation, crunching breakfast cereal, a radio or TV, etc, then they are drowned out.Some of the complaints others have mentioned in their reviews sound a bit like operator error to me. For example, one person said the filter overflowed and sent water over the back of the tank onto the floor. Clearly, the filter was mounted too high....mine are mounted with the top edge 2 inches below the rim of the tank. When the filter pad becomes clogged, it WILL overflow, but into the tank, not out of it.Some describe loud mechanical noises, which sounds to me like a bit of gravel, or perhaps a snail, found it's way into the pump impeller. Yes, this can happen with any filter, regardless of brand, but it's easy to repair. In these filters, the bottom just snaps off, exposing the pump impeller, which is then easily removed for cleaning.And some have complained that the filter "stops working" after some months of service. Again, this is likely due to a need for a cleaning of the impeller and the recess where it sits, where debris or gunk sometimes builds up and prevents it from rotating.On a benefit/cost basis, these filters look really good. They are made of a tough, slightly flexible plastic, so even if you drop one on the floor, it is unlikely to break. Parts for Tetra/Whisper filters are readily available everywhere. And the results are as good as any other filter I've ever used, regardless of cost.The first attached photo shows two mounted in my 75 gallon planted tank, which contains two Nigerian bichers, and two Pictus catfish. The second shows two more in my 55 gallon community tank, with various tetras, cory catfish, and loaches.
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Top reviews from the United States

Reviewed in the United States on September 26, 2018
Size: Up to 40-GallonsVerified Purchase
Customer image
5.0 out of 5 stars How can something so simple work so well?
Reviewed in the United States on September 26, 2018
When you open the box, the Whisper 40i (or it's smaller siblings) don't seem very impressive. It's not much more than a oval plastic bucket, with another bucket (containing a motor and pump) snapped onto the bottom. If you looked at one and thought "this can't possibly work", you would be so wrong.

Perhaps they work as well as they do BECAUSE they are so simple, and so have little chance for things to break. The pump sits IN your aquarium water, so it never needs to be primed. You plug it in, and it begins working, filling the upper bucket, where the water flows through the filter pad and spills back into the aquarium. No priming necessary ever, including after a power failure. When the power comes back on, it just starts working again. It's a shame that every hang-on-the back power filter can't make a similar claim, some unfortunately will lose their prime and/or fail to restart, resulting in unhappy fish and sometimes a damaged filter.

There are no adjustments for flow, so these only run at one flow rate. Inevitably, some food can get sucked up if you let it run while feeding. I have the filters on a separate power strip, so when I feed my fish, I just use the switch on the power strip to turn the filters off for an hour or so. Easy solution and prevents the filter pads from clogging so quickly.

There is no top or lid (unless you buy the model intended for reptiles), so the filter pads just sit there exposed. This means that the water in the filter is fully aerated as it passes through the pads. It also means that no other internal filter is as easy to change pads when they become clogged. The top edge of the pad is above the water line, so you just grab it with two fingers and lift it out. You don't have to disturb the suction cups or hanging bracket at all. You don't have to put your whole arm down into the tank. Maintenance which is easily performed is more likely to be done when needed, so easily changed pads are more likely to be changed when clogged.

You have options for how you want to attach the filter. The box includes two suction cups, and a newly designed bracket which hangs over the edge of your tank. I use the bracket, as it's adjustable for height and I don't have to worry about suction cups losing their suction.

The filter pads are the Whisper bio-bags, which amount to a thick fluffy poly bag, over a plastic frame, with carbon granules inside. Replacing these is simple, and if purchased in a 12 pack from Amazon, cost about 60 cents per bag.

I used Emperor filters for years, and in my experience, these bio-bags work a lot better than the filter cartridges for Marineland products and cost much less to buy. If you rinse them under tap water, which is easily done, the cost is even less. Rinsing the bags doesn't disturb your biological bacteria since they are on a separate part (resembling a hair brush) which remains in the filter when you remove the bags.

You do have some flexibility with regard to media options as well. You don't have to use the carbon which is included with the new pads. You can put anything you want inside the bag, and if desired, transfer it to the new bag next time you change them out. You also don't have to use the separate biological "hairbrush", and if you leave it out, you have room to put another media bag in it's place, with ceramic rings, or whatever else you can think of.

I have four of these, mounted on two separate tanks, one 55 gallons, the other 75 gallons. All four of them are not quite silent, but very quiet. There is a soft, low hum from the motor windings, a little bit like a transformer humming. At first there was also a faint sound like air trapped somewhere, perhaps cavitation in the pump? But these sounds are hard to hear, and not distracting. And the cavitation sound went away on it's own after a few days. I can hear the soft humming sound if the room is totally quiet and I stand near the tank, but if there is any significant sound from conversation, crunching breakfast cereal, a radio or TV, etc, then they are drowned out.

Some of the complaints others have mentioned in their reviews sound a bit like operator error to me. For example, one person said the filter overflowed and sent water over the back of the tank onto the floor. Clearly, the filter was mounted too high....mine are mounted with the top edge 2 inches below the rim of the tank. When the filter pad becomes clogged, it WILL overflow, but into the tank, not out of it.

Some describe loud mechanical noises, which sounds to me like a bit of gravel, or perhaps a snail, found it's way into the pump impeller. Yes, this can happen with any filter, regardless of brand, but it's easy to repair. In these filters, the bottom just snaps off, exposing the pump impeller, which is then easily removed for cleaning.

And some have complained that the filter "stops working" after some months of service. Again, this is likely due to a need for a cleaning of the impeller and the recess where it sits, where debris or gunk sometimes builds up and prevents it from rotating.

On a benefit/cost basis, these filters look really good. They are made of a tough, slightly flexible plastic, so even if you drop one on the floor, it is unlikely to break. Parts for Tetra/Whisper filters are readily available everywhere. And the results are as good as any other filter I've ever used, regardless of cost.

The first attached photo shows two mounted in my 75 gallon planted tank, which contains two Nigerian bichers, and two Pictus catfish. The second shows two more in my 55 gallon community tank, with various tetras, cory catfish, and loaches.
Images in this review
Customer image Customer image
Customer imageCustomer image
269 people found this helpful
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Reviewed in the United States on February 7, 2024
Size: Up to 30-GallonsVerified Purchase
Reviewed in the United States on July 31, 2018
Size: Up to 10-GallonsVerified Purchase
One person found this helpful
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Reviewed in the United States on February 13, 2024
Size: Up to 40-GallonsVerified Purchase

Top reviews from other countries

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Amazon Customer
5.0 out of 5 stars perfect for small tank
Reviewed in Canada on September 8, 2023
Size: Up to 10-GallonsVerified Purchase
Jean d.
5.0 out of 5 stars Excelente
Reviewed in Mexico on July 10, 2023
Size: Up to 10-GallonsVerified Purchase
S Ravello
5.0 out of 5 stars Great filter, very quiet.
Reviewed in Canada on May 15, 2023
Size: Up to 40-GallonsVerified Purchase
MEC Bill
5.0 out of 5 stars Quiet Filter
Reviewed in Canada on April 7, 2023
Size: up to 4-gallonsVerified Purchase
One person found this helpful
Report
Stranger
1.0 out of 5 stars Broken the next day
Reviewed in the United Kingdom on July 6, 2023
Size: Up to 10-GallonsVerified Purchase