AquaClear 20 Power Filter, Fish Tank Filter for 5- to 20-Gallon Aquariums

Before I begin, it is helpful to know the context of this review. I ordered this filter for a 10 gallon, planted tank that is heavily stocked. I had previously only lightly stocked the tank and used a sponge filter as the only filtration, but purchased some extra fish (5 total) and one shrimp so needed something more to handle the bio-load. My setup also has injected Co2 and high lights (~3.5w/per gallon) meaning a high flow rate is needed to prevent algae.This unit is more expensive than the competitors (Marina or Whisper branded Hang-on-back filters (HOBs)), but offers multi-stage filtration that is not included in one "replaceable" filter media. Instead, the AquaClear series separates the biological, mechanical, and chemical filtration media bags, so that each can be replaced separately (or not used at all). This is important because some parts of the filter (the mechanical portion or the bottom sponge) should rarely or never be placed. Filters that combine all three stages in one replaceable filter media will cause mini-cycles in the tank every time you replace the cartridges. By separating the filtration process, the aquarist can replace each stage at different intervals (not to mention switching the types of filter media -- more of this later on) so as to prevent mini-cycling.Setup is fairly easy. Simply follow the instructions included with the unit. The hardest part of the setup is installing the 'leveling device' into the bottom of the unit. If you are not careful, the leveling arm will pop out of the hole when you are trying to adjust it hanging on your tank. Note -- make sure the box your unit comes in is sealed when you receive it. The first unit that was delivered had clearly been opened and used before (in fact there was a crack in the tank). Amazon quickly remedied the problem and provided me with a brand new unit.First lets cover the power of the motor. The output is rated at 100 gallons/per hour. There is an important formula you should know when picking the right filter for your tank. Roughly, your filter should be able to move the entire volume of water in your tank 8x in one hour. So for example, a 10 gallon tank should use a filter with at least 80gallons per hour of flow in order to reduce water pollutants and algae issues. Depending on how stocked your tank is (ie. how many fish and plants you have) you may need to increase that multiple. Therefore this tank is perfect for a heavily stocked 10 gallon tank because it is able to turn the entire volume of water over 10x in one hour. Go with the Aquaclear 30 for anything bigger than 10 gallons. There is a variable flow rate on this unit, but I have never used it. Honestly, the higher flow rate in your tank, the better. The instructions include a way to dissemble the motor and to clean the impeller. I have only had this unit for roughly 3 weeks, so time will tell what the build quality is like on the motor and whether it was really worth the extra cost.Now for the real star of this filter, the filter media slot. The filter comes with three forms of filtration right out of the box: Mechanical (the sponge), Chemical (activated carbon), and Biological (ceramic pellets). I would not recommend using the activated carbon filter right away. Activated Carbon does very little in the aquarium besides remove heavy metals, medications, and tannins in the water. These issues are rarely a concern that you should want your filter to address. Instead, I would recommend saving the Activated Carbon filter and instead purchasing something like Seachem Purigen to act as the Chemical filtration (having Purigen is a must if you plan on overstocking). Hold on to the carbon filter in case you have to treat your tank with any medications. The filter media bay does get clogged with dietrius so be sure to rinse this area out once a week.The only cons I have against this filter is the overall build quality. This filter is not heavy duty and will break if you accidentally drop it or it falls off your tank. That is to be expected though because of how small this unit is. In order to fit perfectly on a 10 gallon (which it does) the unit needs to be small. Just be careful working around it.

I picked up the AC20 for my 10G tank and my initial impression is that I'm pretty impressed with this filter. It ordered the AC because so many people recommended it to me stating that it was a very versatile HOB filter. I was skeptical, but I must say, they were right.The flow rate seems to be pretty accreted to the manufacturer's description. I ordered the AC20 for my 10G tank because it was rated at 100GPH thus giving me a 10x turnover rate. I was worried it would look odd on the 10G tank due its size, but it fits it quite nicely. Its actually smaller than I expected.I like the filter media setup on this unit. There is a three sided basket-type insert with rings on the top to grab pull it out of the filter. You simply fill the basket with media and drop it into the filter. It uses a sponge for mechanical filtration, ceramic rings for biological and carbon for chemical. I don't use chemical filtration on my tanks unless its needed so i left the carbon out of the filter bag and just used the ceramic rings. The sponge sits on the bottom and the rings are on top of that. This is a very versatile setup that would allow you to put whatever type of media in the filter you'd like as long as it fits.The AC20 is a little smaller than I'd like, but it works. The AC30 would probably be the perfect size for a 10G tank. I've seen people use an AC70 on a 10G tank so I'm sure a 30 would fit. I only have a betta in my 10G tank so the 20 works just fine. If you have a lot of fish pick up the 30.I think this is the best HOB filter on the market. Its quiet-, efficient and versatile. My old filter died a week before i purchased this one and my tank was pretty murky and smelly. This filter cleaned it up in less than two days! Pretty impressive for a little HOB. I can't speak to its longevity-I've heard good things-but I will give an update in a few months on the filter.

Works, easy to assemble, quieter than others I have had. Fits my 20-gallon tank.