Undergravel Aquarium Filter for 40-55 Gallon Tanks – Four 11.25” x 11.25” Plates – Under Gravel System for Clear, Clean Water – Safe for Freshwater and Saltwater Tanks (CFU55)

An under gravel is simply one of the best filters you can buy, dollar for dollar. This is because they are highly effective, simple, inexpensive, and last a long time. Here are some tips for how to use this filter correctly. 1. DO NOT OVER CLEAN YOUR GRAVEL. This is the most important thing. You should not clean your gravel much at all. Yes some brown stuff will accumulate. This brown stuff is not "fish poop". It is beneficial bacteria. If you remove this beneficial bacteria your filter will stop working and your fish may die. DO NOT OVER CLEAN YOUR GRAVEL. If you must clean your gravel, only clean 1/2 the tank at a time and give the cleaned side some time to regrow its bacteria before cleaning the other side. Otherwise only very lightly clean the top 1/2 inch of gravel. 2. You do not really need the carbon cartridges. If you want to support Penn-Plax, I guess you could keep buying them. 3. Use 1-3 inches of 1/8 inch aquarium gravel on top of the filter. Under gravel filters are so effective because they provide a lot of surface area for beneficial bacteria to grow on. The more gravel you have the more effective this filter will be. 4. Decide whether you want to use a power head or an air pump to move water through the filter. Power heads will greatly increase the effectiveness of the filter and provide cleaner water. If you plan on having a lot of fish in your tank, you should use power heads. The power heads should be rated at a gallons per hour that is 2-3x the gallons of the tank. If you use air pumps, they should be rated for the size of your aquarium. 5. Decide whether you want to join the under gravel plates or not. If you are using air pumps I would not join the plates. Simply put an air stone in each uplift tube for each plate. You do not need to buy multiple air pumps. Just buy a simple 'T' joint to split the output from the pump. If you are using power heads, I would join every two plates and use one power head per two plates. Some people are complaining that this filter killed their fish which is very unfortunate. The filter did not kill their fish. Incorrect use of the filter killed their fish. They probably cleaned out all the gravel and removed all the beneficial bacteria which caused the filter to stop working. Unless the filter has become so clogged that the water is no longer flowing through it, there is no need to clean the gravel or underneath the filter. If this does happen, I would suggest that the person is greatly overfeeding their fish! Some people are complaining that this filter "produces high nitrate." Producing nitrate is the point of all filters and shows that a filter is functioning properly! If your nitrate levels are too high for you to manage, you are putting too much food in the tank. A different filter is not going to fix this. There are only two ways to remove nitrate from an aquarium: change the water or grow plants. Really the plants are just incorporating the nitrate into their bodies, so you will have to remove some plants eventually too if you want to actually remove the nitrate. There is a reason many successful hobbyist have used under gravel filters for decades and I am very glad that Penn-Plax makes this product!

Works great!! Helps keep our aquarium cleaner

Not sure I would recommend this for an open rimless tank, might be ok with a tank that has a complete lid reason being it takes at least a 30-60gal. rated air pump to run all four air bubblers & then the bubbles coming out the top are constantly popping & its quite loud. Might not be an issue if the tank lid muffled the noise. I think if I run two small air pumps - one for each side running two air stones it might cut down on the noise level since the force of air will be reduced so less bubble force. Other than that product seems good quality.

I’ve been using these Penn Plax Premium Gravel Filters across all of my shrimp tanks, and they’ve consistently proven themselves as a reliable choice. The construction feels sturdy, and the design is straightforward, making installation simple and hassle‑free. Once in place, they fit neatly under the gravel and provide steady filtration that keeps the water clear and healthy. What I appreciate most is the dependability and ease of use. They run smoothly without needing constant adjustments, pulling debris down into the filter bed and helping maintain stable water conditions. For shrimp tanks especially, this kind of consistent performance is important, and these filters deliver exactly that. The materials feel durable enough to last, and the design works well across different setups. Because they’re so reliable, I’ve made them my go‑to option for every shrimp tank I maintain. They blend into the background, but they play a critical role in keeping the environment clean and balanced. A well‑made, dependable gravel filter that’s easy to install, runs smoothly, and keeps shrimp tanks clear with minimal effort. I trust them enough to use in all my tanks, which says everything about their quality and reliability.

I tried everything in my tank to get it clear to no avail! I mean I could barely see my fish in the tank! So I bought this filter and the difference was immediate! This filter is soooo quiet and kinda cute! Made of good quality material and has got my tank crystal clear! Kinda had a hard time figuring out how to get the filters out to rinse off because the instructions are not very clear so idk if I’ll have a hard time cleaning it or not but the price is so good and it works really well I’ll just order another…..not really, I’ll just call the manufacturer to get clearer instructions or google it!

One of the two bottom grid plates was broken--I needed it that day so I used it as best i could. Doesn't have to move under the substrate. Not worth having to send it back. Plastic grid plates are too flimsy. I liked the adjustable air lift tubes. Nice improvement--didn't need to cut the tubes like back in the day. It functions. Does what it is supposed to do. Looks good in operation with the 2 rising bubble columns. Quiet operation.

This is the best filter for old timers. It's easy to use and once was the go to filter. It's hard to find now. It fits my aquarium. In the past, when I used it years ago it lasted many years with only cartridge changes

This undergravel filter is about as cheap as one could make something out of plastic, yet it does the job. I would have preferred one of the "Pro" versions that is made of thicker plastic but the prices are just crazy. I put this filter together, you have to snap or cut out some pieces to join the plates. Take your time or you will crack them. I had to cut the lift tubes a little to make them fit (Allow the hose to be connected and still let the lid fit. I have not used an undergravel filter in some time, I bought this to see if it will make a difference with the black beard algae that I have issues with.