Penn-Plax 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)

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.

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!

Filter seems to work fine and was easy to put together, but one of the stones has something wrong so it is not properly pumping air. Other than that it seems to work. Will update once the aquarium is established and has been in use for a while.

It works great just like it’s supposed to. I didn’t realize how they worked until I set this up. I like it better than having the other kind of filters.

I purchased this because in the past I’ve used it for my tanks in different sizes and I also used a filter that filters the water above and the under gravel filter , filters the bottom of the tank and then I only had to clean the tank once every 6 months or once a year , depending on how many fish/type of fish in your tank , Remember that you still need regular partial water changes and filter replacement. If you do this your tank will be clean/clear and your fish will be happy .

This was easy to assemble and has performed very well and the price is very competitive.

Super passgenau für meine zwei 25cm Becken. Funktioniert wie es soll. Günstig, aber gut.

Very good product

Muy buen servicio del producto, lastima que los tubos de ensamble venían los 4 estrellados, no rotos, lo bueno son funcionales, pero deben cuidar más el empaque porque se nota un mal manejo del paquete o los empacaron estrellados y eso deja mucho que desear de la seriedad del vendedor

Perfect