Penn-Plax Undergravel Aquarium Filter for 15-20 (high) Gallon Tanks – Two 11.2” x 11.25” Plates – Under Gravel System for Clear, Clean Water – Safe for Freshwater and Saltwater Tanks

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!

I have this setup on my saltwater tank as a reverse gravel filtration. It works very well and keeping my substrate clean and my cleanup crew happy.

That it goes under gravel

Simple, hidden effective use of your gravel. You need at least 3 to 4 inches for long term filtration and plant growth. One properly powered uplift tube is plenty for up to 30" inch long tank. Do NOT deep clean bio seeded gravel. A semi-annual light surface vac, and only one third of the surface per week for three weeks.

I like the design how the lock with the two and the gravel filter which is as good I like it and it fits the tank really goodThis is only 15 gallons

Posts were taller than described and water sprayed everywhere. Eventually got them trimmed down enough so the tops are in the water and it’s not quite so noisy. Hope this fixes the cloudy water problem. Really had expected this unit to perform better at keeping the water clear. Other in-tank filters did a much better job at clearing the water without so many water changes.

Was having issues with my water having a slightly yellow tint even though water test results indicated that everything was in the proper ranges.I was told about this type of filter system so I thought, why not try it.Bottom plates are a bit flimsy and one of the locking tabs broke when installing the tubes. I’m not terribly worried about that. The instructions were not easy to read and I just kind of figured it out on my own…it wasn’t that complicated.I’m 2 weeks in with this new system and so far so good. My water is crystal clear and my sweet little fishies seem to be happy. The aerators put out a lot of bubbles (more on one side than the other, but not by much) and it’s a little louder than I’d like, but I can easily ignore the sound of the bubbles…at least I have them and that’s what I want!So all in all…not a bad product!

Arrived on time and in perfect condition. Can't go wrong with these classic filters.

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

Cheapest way to replace parts for a larger system. Worked and fit like a charm.

I decided to go back to old school filtration for my aquarium and bought this for the non-planted area of my aquarium. Having been supplied with two uplift tubes, airstones etc was a bonus. Have had it working for a few months now and it is doing a good job. Although I still need to add more depth to my substrate media.

Very good and simple, but components are a bit flimsy, especially the tubes and how they connect to the plates.

Parfait, exactement ce que je voulais.