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

Don’t give up on an under gravel filter! Still does a great job of keeping crystal clear water. I paired mine with a sponge filter and a small UV Filter. Excellent value for money! Inexpensive does a great job.

This is the only biological filter you will ever need. This simple piece of equipment creates a space of water under your substrate, allowing the flow of water down into it, and back up out of the lift tube.This allows your substrate to be your one and only biological filter, growing colossal amounts of beneficial bacteria, unrivaled by all but the most optimized (aka 20-30 ppi foam filled canisters) power filters out there. Only a big sump filled with K1 fluidized media (has to be fluidized) is proven to really beat it. On top of this, those can get expensive and this product is dirt cheap and super simple. It will also never leak.Now I say that for general fishkeeping. If you keep monster fish or relatively heavier stocked tanks like African cichlids, you might want to look into additional mechanical and biological filtration, preferably the specific power filtration I mentioned.Using the filter the way it’s designed will guarantee you will never, ever have to gravel vac or take this filter down to "clean" it in any way. Higher flow (like with a powerhead) will only increase performance by a few percentage points and might increase your chances of having to "clean" it say, after 10 years.By the way, the brown mulm and gunk in ALL filters is BENEFICIAL and is what is not only keeping your fish alive, but is keeping the water clear and your tank healthy. Minimally clean your filters just enough to restore flow if it gets slowed down too much, and never, ever change the filter cartridges for new ones.That's just a profit driven scam.Using this filter the way it was originally designed to be used by the consumer will result in a zero maintenance filter that will give you beautiful water. People have run these for decades without a need for cleaning.I really appreciate this company for still making this and other old school aquarium equipment.

That it goes under gravel

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!

makes it easy to clean tank

As long as you have used them before they will work well for you

Works perfect

Fit perfect works good