Lee's Pet Products ALE13200 Undergravel Fishbowl Filter, 1-Gallon

This filter is under $5 and is the only bowl compatible filter I have ever seen so there is no better alternative BUT out of the box this filter is completely unusable. Here is the list of steps I did to make this filter usable as the instructions that come with it are extremely vague.First....The filter comes in a box taken apart. The first thing you should do is throw out the plant. It is cheap, useless, and will rip your fishes fins. It's also tacky and there's no reason to attach it.Next.... In order to operate the filter you need a pump and tubing. I purchased the  PENN PLAX Standard Airline Tubing Air Pump Accessories, 8-Feet , this is basic, inexpensive aquarium tubing that is used for everything. Always buy more than you need so you have extra that you will eventually end up using. For a pump I purchased the  Tetra 77851 Whisper Air Pump, 10-Gallon . This pump is WAY too powerful for just this filter. It would be great if you were dividing the pump for multiple things. At my local pet store I purchased the  JW Pet Company Accuair 2-Way Aquarium Gang Valve . This allowed me to control the air flow and make minuscule adjustments. In short get the lowest energy pump you can find and even with that you may need a valve in order to control the air. Use the 10 gallon pump as a last resort.The filter cartridges that come with this are junk and do not work, they need to be altered. Before ever getting them wet, pop the black lid off the top (I used a butter knife, it's a little frustrating) take out the moss, dump the carbon, and remove the bottom moss. Then rise the cartridge and lid out completely and dry them. Put the bottom moss in (a cork helps) I then used  Marineland PA0371 Black Diamond Activated Carbon, 10-Ounce, 283-Gram  and filled the cartridge all the way up but then place the top moss back in and snap the lid on. Then run the filter (bottom side up) under water until the carbon is clean and the water running through it is clear (not black). This carbon works great and I recommend it. You will probably have to replace the carbon every other month or so. You never have to buy the replacement cartridges unless the cylinder breaks as that carbon is junk as well.The stem that comes with this is very high and needs to be cut. It seems as though people have been getting this to fit in a 1 gallon bowl. I personally don't know how as I had trouble getting this to fit my 3 gallon bowl. I cut half an inch off with a sharp knife for my 3 gallon bowl. For a 1 gallon bowl you would have to cut much more.The base is very light and cheap plastic (you get what you pay for), it should really be about 5x as heavy as it is. I purchased an extra pound of gravel to help weight it down which I ended up using about half of. After washing out your bowl or small aquarium you must put this in FIRST before the strained gravel, then dump the gravel on top of it. In order for it to function properly it should be as flat as possible and will probably take up your whole bottom of a bowl. You can then add minimalist decorations, floating ones may be best, this takes up a lot of room.Then fill your bowl/tank up with water and add the necessary water conditioner and beneficial bacteria then allow the tank to sit for at least 20 minutes WITHOUT turning on the filter in order to allow the additives to permeate. Then plug in your filter with the tubing to the small opening in the base behind where the stand gets pushed in and adjust the air flow with your valve. There should be small to moderate sized bubbles coming up through it but the amount of air needed should be judges by you as it varies based on tank size. Allow the filter to run for at least 24 hours to filter the water in the tank. If you see small amounts of carbon come out to begin with that is okay as it will get filtered away but it is important to monitor the filter occasionally during this time to make sure it is functioning properly.I have this filter in a 3 gallon bowl along with a heater with my betta. It keeps the water much cleaner and I now only change 25% of the water weekly. With the modifications listed above it works great. I hope this has been helpful.UPDATE*** So I original wrote that there was no other filter like this that I knew of but it appears that the  Hagen Elite Underwater Mini Filter, UL Listed  works with bowls and is also an underwater filter although I am not sure if it will work with 1 gallon bowls. This may be a filter you want to check out as it seems it may need less modifications than this one.

I'm no longer using a fishbowl after this filter failed to work for me. I was at first concerned with the state of my water, changing it daily, sometimes twice daily, and I bought this in hopes that it would keep my fish bowl cleaner for slightly longer periods of time. As it turns out, I didn't get much use out of this product, so I quit fishbowls altogether.My main complaint is that this filter is a little bit tall, considering it's supposed to fit a fishbowl. How large does your fishbowl have to be then to properly contain this device? I had a 1.5-2 gallon fishbowl and the water had to be filled nearly to the brim to properly submerge the carbon-containing part of this filter.On that note, I read in some reviews that this filter turned the water black and was toxic to their fish. To avoid any incidents of this nature, I pre-rinsed the carbon by running this filter in a separate bowl, sans fish. I did notice that the carbon had some black residue/powder that ran off into my water, and even after cycling water through this filter for several minutes, there were still some traces of water impurity. I wasn't about to take my chances.In combination with the fact that it was overall too tall for my bowl, I did not end up using this product. I switched to a 5 gallon acrylic starter tank from Wal-Mart ($25 altogether, and it included a high-quality air filter, pump, and LED lid light).MORE ABOUT THIS PRODUCT: With this fishbowl filter, I had to purchase a hose, as well as a separate air pump. Overall, I wasn't extremely disappointed with the filter itself, because it probably would have worked if it had fit inside my bowl. The most I lost on this purchase was $7. It was, however, a little irritating to lose money on the pump and hose, as well.Be aware that the base of this filter is completely flat. If the bottom of your bowl is slightly bowed, like mine, the filter will not be securely balanced in your bowl. It sat a little bit crooked in mine, and I had to pile marbles on top of it to keep it from leaning/teetering.I also did not like the placement of the plant vs. the filter on the base. I would have liked it if the filter was positioned in the middle of the base, because my fish would have had equidistant space from the filter stem to the wall of the bowl to swim in circles all around.Also the synthetic plant is made of sharp plastic that could be harmful to some fish with delicate fins/fantails. I removed the plant to be safe.I'm sure for some people, this filter works really well. It just wasn't appropriate for my circumstances.

Don't punish your fish with stale water. This round filter will keep the water moving, and built in filter is easy to clean. The filter has a little bit of flex to it, and I was able to get it into a relatively small bowl.

I took advice from others and modified this to make it work. I wanted a filter system that would fit into a 1 gallon fishbowl. This works. I cut the clear tube down to about 1.5" long with a small saw. I filed a round groove in the base right next to where the tube inserts. I put a slim airstone on the tubing and ran it under the base through the groove and up into the tube from the bottom. I popped the black lid off the filter and dumped the carbon, washed out the filter cartridge, and put back the moss and new carbon from the pet store. I poured bottled spring water through the filter upside down until it ran clear. Then I put the filter cartridge back on the clear tube. I cut filter media to fill the round base underneath then set the base into the bowl. I covered the base with coarse filter media pads, then gravel. This creates a good undergravel filter system with coarse and fine filters under the gravel, and there is still the carbon filter at the top of the tube. The gravel is now fairly deep. I may remove the coarse filters that are lying on top of the base and under the gravel, and that will reduce the gravel level. Now I just need to wait to cycle the system to culture the beneficial bacteria. The whole reason for buying and using this is because after 3 weeks with just gravel and oxygen stones in the fishbowl we hadn't seen any decrease in ammonia levels. (we'd been changing 3/4 of the water daily). The bubbling does make noise, but I think all fish tanks make some noise. Bottom line is that this can work for a filter system for a fishbowl.