U3 Underwater Filter – Designed for Freshwater and Saltwater Aquariums, Also Ideal for Terrariums and Turtle Tanks

Purchased this filter nearly 3 years ago and it’s still going strong - we’ve not had one issue with it. Replacing the filter pads is super easy & they’re readily available. I love that it’s completely submerged so it is 100% quiet - no humming, bubbling or taking up space hanging off the back of your tank. Yes, it takes up some space inside the tank, but if you put it in the back corner you barely even notice it. You can direct how you want the water to flow out of the filter as well - from the top, middle or bottom - depending on the needs of your tank. I would definitely purchase again if for some reason this one craps out.

The Fluval U3 Filter is a very good underwater filter. It does a good job keeping the water clean. There are adjustable flow vents so you can adjust how you want the water to flow, and you can change it anytime with a turn or a twist. It is very quiet underwater, and changing the filter and filter media is quick and easy. You can do it all underwater pretty much. The filter media can add up if you don't buy it at a good price. Amazon does have some good pricing and some items are sold in bulk which make it cheaper. The bio-media you only change half at a time so to not destroy the cycle you have in the tank. The filter sponge can be squeeze rinsed in a bucket of tank water to remove the yucky stuff at put back. The poly/carbon cartridge i the only think you need to replace completely. You can try to squeeze and rinse out the poly/carbon in a bucket of tank water to buy more time with it, but the poly and the carbon side may both be less effective over time. As mentioned, these things can be purchased in a bulk quantity on Amazon for a great price saving you a lot of money. I recommend the Fluval U3 Underwater Filter because it works great and is very quiet where you here nothing. No more crashing waterfall from your overhang filter. Amazon usually has one of the best prices on the Fluval filters. If you have Amazon Prime, the 2-day Free shipping is a huge money saving plus.

Old review: Best filter for a turtle that I have found. This is my second one and would recommend the product to all turtle owners. . Revised review: This is now my third filter which was purchased to replace the second filter that I discussed above. I purchased the second filter on 10-24-16 and the third filter on 11-12-16. . The second and third filters are functioning below the standard of the original filter that I purchased a few years ago. The filter cartridge design appears to have been changed and the modified design restricts water flow considerably. As a result of the restricted flow due to a redesigned and smaller filter cartridge water inlet opening area, the filter clogs in half the time of the original filter and only half of the filter media sees direct inlet water flow. (When replacing the media only half of the media is dirty) I use this filter on a 50 gallon aquarium that is 60 percent full with water. This water level is sufficient for my turtle to swim and exercise. The original filter cleaned the water beautifully and required change out every 4-5 weeks, the new models require change out every 2-3 weeks. . I have modified the filter media housing (blue) by cutting additional openings to allow more water flow through the media. The modification has returned the functionality of the filter back to the original design and is working well. Change out every 4-5 weeks. . Do not purchase this filter for use with a turtle. As you can see I previously backed the original filter (design) for turtle use however, when this one fails I will look for another manufacturer and design. Very disappointing, I probably recommended and sold 5 of these filters throughout the years.

This is probably an atypical use for this filter, but I’ve placed it in a small (50 gallon) planted outdoor fish pond, and so far it's worked great. My requirements included: Submersible design that could sit at the bottom of the pond, low enough wattage to run from a battery pack (the kind you use when traveling with a cell phone or laptop), and adjustable flow so that I'm not blasting my little minnows around too much and kicking up too much sediment. The U3 met all of these and at just 6 watts, runs for about 6 hours on a 20000mAh battery. I leave it out in the pond and just run it when I begin to see debris particles floating in the water, which ends up being about 1-2 times per week. I don’t put any chemicals in the pond and have avoided algae blooms. Phosphates, ammonia, nitrates, and pH have remained good, according to weekly tests. The only surprise, compared to another brand of filter I tried, is that the U3 is buoyant enough that I have to put rocks on it to get it to sink to the bottom of the pond since the ground obviously isn’t glass like an aquarium, and it doesn’t stay suctioned to the bottom. Although the minnows can survive in very low oxygen environments, because the weather is hot and the pond is so small, I do run a separate USB air stone for them that lasts up to 48 hours on a battery pack. The combo of this and the U3 have kept the pond naturally pretty and habitable for small fish. The only downside is that the Fluval does suck up pieces of mosquito dunks as they dissolve... not sure if they still work if they're stuck inside the filter somewhere. I can’t speak to how it works in a normal aquarium setting, but it's a convenient way to keep a small pond looking nice and doesn't necessarily require an electrical outlet if you don’t want to run it constantly (I suppose I could run it as much as 6hrs every day if I brought the battery in to charge as soon as it was depleted). 6 month update: This little filter is a beast. I’ve bee using it clear the gunk that’d built up in the pond all winter, and it handles sediment, decaying worms, and algae without complaint. I’ve temporarily put activated charcoal in the center compartment instead of the ceramic pellets to try to deal with the water discoloration.

I like the idea of this filter but it just didn’t do what I wanted. The amount of bio media that you can fit in these is so small you might as well just put filter floss in there. I also really wish you could use more than just one of the flow options at a time. The filter is really easy to clean and really couldn’t be any quieter but I think you’d have a hard time using this as your main.

I live Fluval as a brand. They are the one I trust the most. This is my second underwater filter, only in that I had to go with a bigger tank. It’s easy to set up and the underwater part makes it silent!

I bought this filter because I currently own six Fluval FX6 cannister filters and have always been highly satisfied with this brand. I also needed an extremely quiet filter as this particular aquarium sits as the backdrop of my work desk. First the good: 1. This filter is utterly silent. It sits completely submerged in the tank and therefore cannot be heard at all. Every so often I have to check it to see if it's even still running. 2. This filter does an amazing job keeping the tank clean and clear. I set up an aquarium on the first day with Aragonite sand that had not even been rinsed, got the filter up and running and within 3 days the water was crystal clear (mind you, I am slightly over filtrating a 20 gallon with a U3). 3. It's very versatile in the different ways it can be configured. Now the (very) bad: The Fluval U3 Underwater Filter Poly/Carbon replacements are $8.99 EACH and you have to replace TWO of them once a month. I am kicking myself for not checking this prior to purchasing this filter, as that is just an outrageous amount of money to spend on monthly maintenance for one filter. What's worse is that I can't seem to find any off-brand options for the U3. This is a total deal breaker for me when I can get a Tetra Whisper In-Tank 40i for $16 that is equally as quiet and does a comparable job cleaning the water while only spending $8.45 for a year's supply of poly carbon replacements. For that simple reason, I'd take a hard pass on this one and go with something that has a more reasonable cost of operation, and that won't not set you back $20 per month to keep it going!

Works great for a 20 gallon tank with Molly's

This is a long term review as this exact filter was bought April 2018 and used yearly/monthly/weekly/daily/hourly/minute by minute ever since ! I've been a Fluval customer for decades, I've had a number of their filters with dozens upon dozens of tanks over the years and what keeps on me being loyal? 1. Quality 2. Dependable 3. Does it's job day in day out I've been in the hobby for decades and have kept salt/fresh bare bottom/planted and everything in between. I've given speeches, helped 100's of people in this hobby and in all that time and experience you can easily weed out poor manufacturers and you quickly gravitate to manufacturers who provide that dependability that is DEMANDED with the aquarium hobby. In all my years I've never had any Fluval filter quit working for me. Personally I'm in the underwater/submerged phase of tank keeping I guess you can say. I've converted all my main tanks with the Fluval U series and three tanks have this same Fluval U3 for a few different reasons, most importantly is for it's silent operation. I have a couple tanks in bedrooms and the old HOB Hang On Back type filters tend to let the water drop too far as to create that waterfall noise. Some may like that noise but I call it noise for a reason. With the underwater series such as this U3 there is zero and I mean ZERO noise from the filter. No fish stories here so I included the three U3 series filters as proof. For the filter itself, you can adjust the outflow in various regards, the filter unit itself clips into a holder which is suction cupped to the aquarium glass wall and opening the top door to change filter material is quick and painless. If the filter does not sit well in the filter cage something is just blocking it a tad, most likely it is the power cord so just rerun the cord past the clips on the back of the filter and your good to go again. TIP ► When doing any tank filter maintenance I strongly suggest to turn it off first. When I do filter maintenance I completely remove the entire filter into a bucket and then open it to change out filter pads. I do this because if you change filter pads in the tank and plug the filter back in, debris will shoot out of the filter like a hurricane. Change out filter pads in a bucket, rinse the filter itself in some water and you've minimized the debris hurricane. TIP ► There are 5 basic areas within the filter. 1. The ceramic media. Never clean this part...leave it nice and dirty. Caked in debris isn't needed but if there is just remove that debris, don't try to 'wash' the ceramic rings. They also don't need to be replaced. If they are turning into powder, sure but in all my years I've never had to replace ANY ceramic media ! 2. On either side of the filter there is a course then fine area. The course is the sponge and material is first trapped into this. When you do your REGULAR maintenance squeeze this out in water only. You don't need to replace this as the sponge will last for many, many, many years. 3. The final stage is a bad that 'polishes' the water and this includes activated carbon within that filter pad. In my tanks I don't run activated carbon and I caution against using that in most cases actually, so when my filter pad gets dirty I only squeeze this filter pad out in water and I don't replace it. The filter material's integrity against the plastic filter pad cage will last for years and years. People replace their filter material much too frequently. Sorry aquarium filter manufacturers... But they all tend to advocate replacing the filter material wayyyyy to frequently. Replacing filter materials is a huge profit maker for manufacturers. TIP ► In doing filter maintenance when a filter sponge or pad needs to be rinsed some people state to not use tap water as it contains chlorine and possible chloramine so those people say you should only rinse out filter material in cycled tank water. For my own practice I use tap water and I'm never concerned with the tap water chlorine or chloramine. TIP ► In doing filter maintenance only do ONE SIDE at a time. Since the beneficial nitrifying bacteria is held in the filter material if someone were to 'clean' the entire filter - all filter material, the tank can be put into a mini-cycle. Not really a good thing. Only clean 50% of the filter per time, doing this will give a more chemically stable aquarium. TIP ► A dirty filter is a wonderful filter. While you don't need to live with 50% water flow rate from the original brand new condition, people hurt their tanks by cleaning filters too frequently. The nitrifying bacteria is held in the filter material so cleaning the filter too often will easily cause a mini-cycle which will always put stress on livestock. Crystal clear water = dirty filter. Clean filter = zero cycle. Might sound strange but it's the truth. TIP ► If you hear the word ' cycle ' with this hobby that is in reference to a naturally and beneficial occurring chemical process where ammonia is converted to nitrite and then over to nitrate. A brand new tank will take aprox 30 days naturally for this to happen. At that rough 30 day mark PPM readings will be 0 ammonia, 0 nitrite and a reading of nitrate. In terms of fish you need really nothing for nitrate so your reading can be low however if you have live aquarium plants a reading of nitrate is mandatory. TIP ► In all my impeller filters, right out of the box I use a small dab of 100% pure petroleum jelly and rub it all around the magnetic part of the impeller. This will help with lubrication and a small tweak we can do to even further make the tank more quiet. Not gobs are used just a thin coat. I've done this for a very long time and there have been ZERO negative effects in any of my tanks. If this is not done, that beautiful slime coating found in mature aquariums will form within a couple weeks and naturally coat the impeller. I still just use the petroleum jelly anyways. TIP ► Please be very careful about filter placement especially if someone has fine substrate material especially such as sand. This can easily get sucked into the filter and once it hits the impeller it could easily give a louder grinding sound. When people come to me about grinding filter noise this is the first thing I ask them to check. Make sure the impeller cage is 100% clean of any debris. I typically say no closer than 4" so the substrate bottom when people have those fine grain substrates. Standard type gravel size which I only use, I can let the filter stand right on the substrate itself. TIP ► If by chance you have any sort of filter that the impeller appears to be caked with material and cannot be washed off just use a fine piece of sandpaper. Something like a 200 grit is what I have used in the past to make sure there is nothing 'stuck' on the magnet that can cause unwanted noise. This goes to any brand of magnetic impeller filter. You don't need to grind the magnet away just make the surface clean once again. TIP ► My first tip above talked about a dirty filter being wonderful and people clean it too frequently. This is 100% the case...however if your filter requires cleaning more than every 2-3 weeks then it is not the filter but the tank itself has a maintenance issue. If could very well be a buildup of mulm/detritus from lack of regular tank maintenance. Your filter will collect floating debris however if there is too much floating debris then any filter no matter brand or size will clog. That is our issue not a filters issue of not functioning properly. An aquarium filter's purpose is to COLLECT floating material not to magically make floating material 100% disappear. It is OUR regular maintenance job to remove that collected material. TIP ► A simple way to see if a filter is working properly, HOB, underwater or whatever is if water is being moved by the output. If water is being moved, the filter itself works. If the water is only moving 50% from original flow rates that means it is a very dirty filter that needs our cleaning maintenance...the filter did it's job just fine as it collected the floating material....the 50% flow rate is our issue with tank maintenance. There is much more I can write but I'll cut it off there. Good luck with the hobby, keeping aquariums is a wonderful thing. This brand is legend...please don't let someone else tell you otherwise. ===================== Overall: 10/5 Yes a 10 out of 5. Fluval filters are amazing. Suction power: 5/5 Easy to clean: 5/5 Noise level: 5/5 ===================== Helpful, is how I hope you find my review

Fantastico, istallato, in un acquario da 80 LT, con 40 piante vive, sottofondo fertile, ghiaia e accessori, legni e rocce, fatto partire al riempimento, non ci potevo credere, solo dopo un giorno l'acqua era limpida e cristallina, ora dopo 20 giorni i parametri ( pH, e vari sono tutti nella norma) ho fatto una modifica, cioè ho aumentato di capienza il filtro biomax, aggiungendo altri canolicchi, fantastico, l'acqua non ha nessun odore, e devo dire che è molto silenzioso, non si percepisce nessun rumore, filtro adatto a mio parere anche x acquari superiori ai 80lt, diciamo fino a 120, sarebbe perfetto, erano anni che non allestito un acquario, e devo dire che dopo essermi fatto un bel giro di informazioni in merito, la scelta e stata più che azzeccata, lo consiglio vivamente, molto comodo anche il poterlo ispezionete,e pulire, accesso facilitato...FILTRO PROMOSSO...5 STELLE.

Efficace.. silencieuse. Elle fait son travail.. aquarium de 150 litres. J'en ai acheté plusieurs, aucuna a été aussi efficace et silencieuse.. si un jour elle lache je reprends la même

Filtret är tyst, och har bra filtrering och att det även finns ett fack för biomedia är ett +. Och enkelt att rengöra med sin endelnig av 3 fack man drar upp ett fack i taget, så biomedia facket i mitten kan man låta sitta kvar så bakterierna behålls om det inte är igenkleggat.Att kunna välja utblås överst, spraybar mitten utblås botten är ett plus med.

Très bonne pompe en 6 h eau cristalline 👍👍