Penn PLAX World Aquarium Filter, Small

I used these several years ago for small fish tanks. Then it got to where I could no longer find them at Walmart or other stores. So I was glad to find them at amazon. The cylinder shaped round tank in the photo I attached is only about 8 inches across. And the under-gravel filtration that was included with the tank didn't have filter fiber or carbon. So the Penn Plax filter was just the right size for the extra filtration I needed. And the replacement cartridges were a very reasonable price in a 6-pack.

This is a great betta filter, with a few modifications. This filter is small and unobtrusive. It fits my 1.5 gallon quarantine tank and 3 gallon tanks well. I popped off the backs of each filter cartridge and inserted ceramic media on top and the sponge stays on the bottom. After cycling, the sponge and ceramics get rinsed every few weeks in the old just removed tank water (never tap water) so the beneficial bacteria doesn't die. I can slip in a piece of carbon pad with a section of the lower sponge and just replace the carbon every other week. Never need to replace the plastic cartridge. I just place the back on again and secure with a rubber band before popping it back into the holder! My betta are not bothered by the gentle bubbling and even like to rest on top of it. The bubbles give adequate suface disturbance for 3 gallon or under tanks. I am very pleased. I now have basic 3 stage filtering for my bettas.

Perfect for 1-3 Gal tanks.I have 2, one in a 1.5 and the other in a 2.5. Both work great and have had no issues.I would not recommend to use this in anything bigger than a 3 gallon tank, you'd need more suction and flow force to circulate the water and evenly filter all the water. This is for a single fish (betta) or smaller schools of fish such as a few neon tetras, grow out tank, platy's etc etc. I'm sure we all knew that already but some reviews are saying it's weak or that it doesn't do it's job but are using it in 5+ gallon tanks lol.If you want a small filter to use in a 1-3 gallon tank, look no further.

Isn't a bad filter at all! I run nano tanks (10gals and under) and most of my tanks are heavily planted. There is carbon in these filters which makes it difficult to add fertilizers since carbon will absorb most liquid fertz but that's honestly my only complaint. I am looking forward to using these as travel filters when I need to transport live plants and fish to shows and events. Overall not a bad filter for the price! I will add that these filters are LOUD. Mind you I hooked up the air line from a large air pump and they got a full blast of air from each line. The bubbles coming out of the "out take" area are large and make a loud popping noise so I had to cut the lines and add an additional control valve. Other than that, these filters are great! Will purchase again!

Good construction but poor design. There's a back channel the air just flows straight up through and bypasses most of the filter pad or carbon. Since there's no air stone the bubbles are full size and have to hold back even the smallest air pump. Still give 3 stars since in suck a small tank like it's advertised for, just a LITTLE water flow over the pad a stones seems to be enough. Berta fish is much happier than the waterfall filter pump which came with the Berta tank to begin with.

Update 6/15/18: I no longer care that these are loud. It's by far, the most effective filter I've ever used. My fish tanks are crystal clear, my fish are happy, and these are very easy to switch out for clean filters. I increased the rating from 3 stars to 5.Update: As one other buyer mentioned, these are loud. I actually bought a fish tank and fish to provide "white noise". These are a bit loud for my taste, but are doing a nice job keeping the water moving and circulating in the tanks, and the fish don't seem bothered by the increased current.I will update this review once I see how well it works, but for those thinking of buying: Make sure you have a length of air tubing to replace what it comes with. These arrived with a crimp in the tube, and it prevents air from moving freely.

This is a great little filter for 2.5 to 3 gallon betta fish tanks. It has strong suction cups and can work right side up or sideways. This is only the filter unit, so you will also need an air pump and tubing to get it to work. It gets 4 stars becuase on full power, this has too strong of a current for bettas, so you will need to buy a control valve for the airline tubing to reduce the power. That being said, you can then adjust how light or strong you want the flow. I replace the cartridge every 3-4 weeks. This is the best small filter I have used, and I’ve tried several.

I had been using one of my 5 gallons for extra plants. Admittedly, it had been neglected for several months and desperately needed a water change. After an ~80% water change, the water was still cloudy and a bit stinky.I popped 2 of these in the tank overnight and it's like a new tank! I wasn't expecting much since they're so small, but they're mighty.My only complaint is that for some reason, the tubing for my air pump doesn't fit very tightly on one of them. It's very strange. I tried a couple different pieces of tubing and it seems like the part the tubing goes on is just a bit smaller on one of the filters... I eventually got it positioned properly so the tube stays put so it's not a huge deal.