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

There are many choices out there when it comes to filtration for your fish tank. Which of the many choices out there would make the best choice for you? Internal, or external? Are you looking for supplemental filtration, or primary filtration? In most situations, an external filter would be the better choice. Canister, power filter, wet/dry sump, refugium, all have the advantage of not taking up any space inside the fish tank. They are also all capable of holding more media than internal filters. However, some situations make it difficult to install an external filter on a fish tank. For example, if the tank is located in such a way that there are no available spaces behind, nor at the bottom, then your only choice might be to use an internal filter. For simple biological filtration, an air-driven sponge filter would suffice. However, a pump-driven internal filter offers increased circulation and better mechanical filtration. Let us say that you want an internal filter that is capable of providing complete filtration. Not just supplemental filtration but rather a single filter that can provide mechanical, biological, and chemical filtration. In that case, your choices will be limited. Most internal filters are designed to provide supplemental filtration. Most will provide mechanical and biological, but few of the designs will provide chemical filtration. The Fluval U-series of internal filters provide complete filtration, with the exception of the smallest model in the line up. This is the best internal filter that I have ever bought. An internal filter would not be my first choice. However, I was faced with a situation that would not have allowed the use of an external power filter. My choice then came down to between an internal vs. a canister filter. The tank will contain floating plants. Circulation needed to be gentle, and the surface of the water should be still. This filter met the requirements, without the maintenance hassle of having to use a canister filter. The filter was easy to install. The bracket system allows you to remove the filter, without having to remove the suction cups. The suction cups are attached to the bracket, and it is the bracket that holds the filter unit inside the tank. It is surprisingly quiet. You can adjust the output. Water can exit from the top, the middle, or the bottom of the unit. The middle output provides the most gentle flow. Mechanical filtration is provided by a coarse sponge, followed by a fine filter pad. The back of the filter pad is carbonized. This provides a little bit of chemical filtration. Biomax ceramic rings provide the biological portion of the filtration. All in all, a tidy, complete filter system. Disadvantages? It takes up a lot of space inside the tank. The small amount of carbon bonded to the filter pad is not enough to remove tannins from the water. And, it gets used up very quickly. It is possible that you may be able to remove the biomax and put pelleted carbon in its place. Another weakness is that the mounting bracket uses suction cups to attach to the tank wall. A truly modern filter design such as this should be using magnets instead of rubber cups. If you can use an external filter, that should be your first choice. They provide advantages at all three types of filtration (mechanical, biological, and chemical) over even the best internal filter out there. However, if you must have an internal filter, then this is the one that I would recommend. Any of the Fluval U-series, starting with the U2, all the way to the U4 will provide complete filtration. The smallest model, the U1, will not provide complete filtration. Highly recommended. This could be the best internal filter system available in the hobby, in the humble opinion of this reviewer. Please know that I do not own every model of internal filters out there. I am basing this on the ones that I have owned over the years, but there are a few models that I have not tried. However, I have researched the ones commonly available in the U.S., and this line appears to be the best out there. Consider your needs carefully before you decide. If ever Fluval were to discontinue this model, then you will find it difficult to find replacement media. It is not as easy to "create" your own media for this as it would be for an Aquaclear. But it can be done. You can buy bulk padding and cut them to the approximate size and shape of the plastic holder. For carbon, you can simply replace the biomax with large, pelleted carbon.

The Fluval 2 Water Filter is designed to work in a variety of configurations. This makes it absolutely perfect for tadpole tanks. You can put it sideways, just beneath the surface of the water. This creates a long "basking area" that the tadpoles absolutely love, while at the same time keeping their tank clean. I had no idea the Water Filter would be so ideal when I bought it. Sure, I knew it had a great reputation as a water filter, and that it could create a gentle stream. That is of course the big challenge with tadpole tanks. Tadpoles are MESSY - but they are also tiny and delicate. You want a filter that moves enormous amounts of water in order to keep the tank clean. At the same time, you don't want industrial-strength jets of water blasting into their swimming area. Especially when tadpoles are just developing their little arms and legs, getting hit with that water blast could cause all sorts of damage. The Fluval 2 Water Filter is very easy to set up. You decide what kind of output stream you want, set the speed, and voila. You stick the whole thing into your tank and you're set. I put it in sideways figuring it would take up the least amount of swimming space that way. I was completely shocked when I came back a few hours later and found six of the little tadpoles had wriggled their way on top of it and were soundly sleeping there. At first, I was worried. Would a little limb get stuck somewhere? Would the soft buzzing bother them? But no, it almost seemed soothing. They actively wrestle with each other to get onto that spot and, even if others come and pile on top of them, they lay there contented. It is really cute to watch them. They're like a pile of kittens. The water in the tank is absolutely much cleaner with this running. It does the best one could hope for against the output of these industrious little baby frogs. Highly recommended for tadpoles. Just install it sideways, just below the surface, so the little tadpoles can rest on top of it. There's lots of photos and videos of this in action all through the SuttonMass site. Ask if you have any questions!

I can't actually provide a rating on the performance of the filter itself. It arrived in its usual, timely manner with Amazon's excellent shipping. The shipping package and the display box themselves were in great shape. Upon opening the box, I was treated to a cloud of dust. The bag containing the bio-pellets was ripped wide open and the pellets had disintegrated, coating the unit and the box alike. In addition, one side and the top of the unit looked as if they were kicked around before being packaged. There were scuff marks and deep scratches all over the exterior. Not only did I get a nice dust cloud, in the bottom of the box there were several plastic pieces rattling around. This is never a good sign, but being green in color and the unit itself being black, I didn't think too much of it. That is until we cleaned the unit off, installed it in the aquarium, and turned it on. Nothing happened. It hummed like it was running, but no water was being pulled in or pushed out, even after trying all of the settings. I took the filter out and disassembled to see what was going on. To my surprise, I was able to identify the loose green plastic pieces as the impeller blades. Which means that, unless they used magic plastic, the impeller fan-blades were snapped off prior to the unit being assembled, the broken pieces were dropped into the box, and it was shipped to me. I've been using Amazon since the dawn of...well, Amazon. Never have issues with books, most of the time movies and games come in good shape. Everything else always seems to have an issue, though. My board games had crushed boxes, making them look used. Our sound bar worked for a few months before the optical input and power link functionality just died randomly. Now we order a filter that was assembled broken and shipped. You can roll the dice on this, or just give the money to your local pet store and help them instead.

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.

This is one of the best Underwater Filter's that I have found for my turtle tank. Bought for a redear slider. in a 30 gal tank. As soon as I put this in the water, the water cleared up, it is very quiet. The filter is easy to clean. I can get about a month with spot cleaning before I have to pull the filter and do a full clean out. So glad that I found this filter because turtles are very messy!

Be forewarned; this is a rant. I've had internal Fluval filters for years and years. The older models were simple, easy to use/clean and quiet!! I recommended them to anyone with planted, low-stocked tanks that hated to see equipment hanging all over. Now, they've been "improved" upon beyond usefulness. I still think they are one of the best internal filters on the market. Excellent water filtration, great options for filter media, nice to have 3 options of water flow (all top, all bottom or a vertical tube for middle flow). As a filter and quietness, it rates 5 stars -- ease of cleaning, 1 star, thus the 3 stars in the middle. But due to all of the little "quirks" you have to deal with in getting it cleaned, I'm looking around for a different brand that doesn't waste my time. Instead of quickly cleaning the filter and moving on, I have to block out big chunks of time simply due to poor engineering. Frustration-free they are not! The theory: To clean/change out the filter, pull filter from wall bracket, lift out. Clean. Return to bracket and push bracket closed, close the filter lid. Minimum fuss; no scrubbing of the hands/arms before putting them into the tank. Sounds easy. In reality: Because the filter is difficult to pull out from the wall bracket, I usually end up pulling the wall bracket out too (which means I've had to delve into the water to loosen the suction cups for the wall bracket -- gotta hand it to Fluval, their suction cups are sturdy and hold extremely well -- so it's a battle to release those cups). Because the power cord is now wound thru bracket slots on the back of the filter, I suspect the cord keeps the filter from easily sliding in and out of its bracket. OK, back to cleaning: In order to open the bottom propeller section for cleaning, you have to unwind that slimy wet cord from its bracket slots on the back of the filter. Once cleaned, you have to rewind the cord back into the slots - difficult to do as everything is a very, VERY tight fit. Yes, you do have to rewind the cord back into the slots -- the filter won't fit back into its bracket otherwise. Keep in mind that the bracket slots have created a permanent slight "S" curve to the cord, so when you re-wind it, you gotta get those curves put in the same position. If you are just changing/cleaning the filter and not dinking around with the propeller, you still have to pull it out from the wall bracket. Once you've opened the top cover of the filter, it tends to be difficult to snap it closed again. Remember, you paid for a system that you can easily change/clean the filter quickly without getting your whole arm wet. This is not that.

__________________________________________________________________________ UPDATED 7/26/12-- see bottom part of entry-- upgrade from 3 to 5 stars __________________________________________________________________________ Original review June 2012: I'm writing a long review because I found it helpful to hear others' experience specifically with turtles. They are a little different than fish when it comes to what works. I have a painted turtle, about 5-6 inches long right now. We have an algae eater too who helps keep the tank clean (we call it a sucker fish, not sure what its real name is). We also periodically add small minnows and goldfish to entertain the turtle and for food if we forget to feed her or go on vacation. Since she's primarily a water turtle, her tank consists of mostly water with a few haul out spots. We just upgraded from a 20G tank to this one. Previously we've always used the Whisper Quiet filters with great success. People would rave about how clean the turtle tank was, and we could pretty much ignore it (don't worry about changing water, etc.) In the 20G tank we had the 20-40G Whisper Quiet in about 16G of water, no plants, a few submerged items, and a floating plastic "log" for basking. For the 50G, we added a few more submerged and surface items, but all are plastic or rocks, nothing living. Upgrading to the 50G tank (with about 40-42G water) posed a problem for me. All of the larger hang on back filters required the water level to be higher than I wanted, since the turtle needs some land, and I didn't want it climbing out. I tried rigging a few up-- the larger Tetra one worked very well, but I had to rig it inside of the tank, and it just took up too much room. I decided to try the underwater Fluval for two reasons-- never need to worry about water level, and because I'm not willing to invest in a canister filter. PROS: --silence. it's golden --ease of changing filter media (it's really simple, you can lift it up so you don't contaminate everything or spit junk back out) --will never dry out or burn out if you lose power and it restarts (since submerged) --ability to place where I like in the tank for optimal filtering and flow to stir things up --ability to change parts of filter at a time to preserve beneficial bacteria --foam pad separate from other pieces so you can rinse that and not everything --no splashing, so no hard water stains on side of tank CONS: --I want to love this filter and I hope it works long term. We used it in a tank that had been recently filled and set up, with the Tetra running for about a week. Initially this worked really well, but about a week into it, the water turned nasty green. First off, TURTLES ARE DIRTY. By nature I don't think this filter accomodates that. I'm holding off judgement since it sometimes takes a while to get things right when you set up a new tank, as it happened before with other filters too at times. However, in this case, I think it's because of a lack of active carbon in the filter. There is just a tiny bit there, and in my experience (6 years with this turtle), the active carbon is ESSENTIAL to keeping them from getting stinky and gross. I decided to remove the bio pellets from the middle part (step 3) since I never had them before in my tanks anyway, and instead fill that space with one of the tetra filters filled with activated carbon. It's been about 10 hours. The nastiness is gone and the tank looks much better. There still seem to be a lot of particles in the water, but I am continuing to work on that-- not sure if I can blame it on the filter at this time. I will keep adjusting, because I think this filter is worth figuring out how to make it work for turtles. I gave it three stars because it advertises that it can be used for my purpose, but I don't think it comes through with the media it uses. I also think their media replacements are expensive relative to other filters (which is especially frustrating when they aren't even working for me). However, if the makeshift adjustment of using other carbon filters inside the third chamber is effective, I would upgrade to 4 stars. If I get to perfectly crystal clear water without the need to pay attention to the tank every week (yes, it's possible with some cheap filters), I'd go to 5 stars. I ask a lot from my filters! ___________________________________________ UPDATE 7/26/12 This definitely deserved the upgrade to five stars. I had to leave for three weeks after adding the Tetra carbon filter to the center in place of the bio pellets, so I filled it with a bunch of minnows for her to eat over time, then came home to a tank that was still crystal clear after 24 days. (Trust me, I was almost afraid to look at the tank when I returned for fear of how gross it might be.) A few minnows were still swimming around happily too. I went ahead and swapped out the carbon filter, but it looks like I can simply wash out the outer sponge and pathetic carbon insert supplied with it periodically and replace the Tetra carbon insert in the center chamber monthly. I still don't like that I had to adjust it, but I don't think there's a great product out there for turtles, and this is working VERY well. Plus, I am now purchasing the cheaper Tetra filters, so my ongoing costs will be less. If you go this route, it does seem like a very tight fit to fold over the Tetra filter and slip it in the middle chamber, so don't be shy. Just wiggle it as you push it in and be gentle. All that remains to be seen is longevity, but for now I am one happy consumer!

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.