Very good small filter for its cost. I replaced half of the the sponge filter that is provided with the kit using other bio media and love it. I use 2 of these with a 55 gallon tank. It would be great by itself for a 10 gallon or a 20 gallon. The best part is that you can put the canister out of sight so your tanks looks less crowded and messy than using most other type filters. I would have given this filter 5 stars but for 2 problems. First the green tubing that is supplied if extremely difficult to attach to the other connectors. I heated the tubing in boiling water for a while to make it more flexible so it would stretch over the plastic connectors, but it was still extremely hard work getting them all attached. I'm a big strong guy, but I have problems with arthritis in my hands that made it nearly impossible. It took me a couple of hours. If you don't have strong hands, this might be a problem. I would have gone to the hardware store for replacement tubing that fit more easily, but I started working on it late one evening after stores were closed and wanted to finish it rather than wait. Yeah, I one of those guys that before GPS used to drive around forever lost rather than stop and ask directions. The second problem might not matter with some tanks. With my tank the plastic parts did not fit well that hang on the back edge of the tank to hold the intake and output lines. They are "U" shaped connectors through which the water passes over the back edge. The plastic rim around the top of my 55 gallon glass tank is too wide to fit between the narrow notch in the "U" shaped connector. I'm planning to replace these with some PVC plumbing connector when I'm next at the hardware store. My tank is 35 years old, so modern tanks might be designed differently so this might not be a problem. Since lots of the green tubing is supplied, right now I've just drooped the green tube over the back and into the water. Until I get some PVC connectors for a better solution, I've just fastened the green tubing using a suction cup and some small zip-ties to keep the hoses in the water. The problem long term with this solution is that the green hose is gradually collapsing and closing shut where it hangs over the back edge, which is why a rigid connector is needed to pass the water up and over the back edge, both to and from the filter. If you have semi useful DIY skills this is a great little filter. Its far easier and better than the many DIY videos on how to make a filter using soda bottles. It is Infinitely better and worth the cost. If you include the cost of a pump with those "free" DIY filters, this filter with it own pump doesn't cost much more than a good air pump to use with the DIY types. If cost is not an issue, and you want something that works straight our of the box quickly, this filter might not be it. If you don't mind tinkering a bit, this filter is super for its cost. The canister holds about a half gallon of media. You can use the supplied sponge filters by themselves or replace some or all of the sponges with whatever bio media you prefer. I put ceramic tube type in one, and bio balls in the other. If you have a 40 or 55 gallon tank, there are larger sized version of this SunSun filter that would work better by themselves. I bought this one and then decided I wanted more capacity and ordered another. It would probably have been easier to have ordered a single larger one if I had planned better. If you have any small fish, especially live bearers like guppy, platty, or molly, I wold suggest a pre-filter on the intake to keep fry from getting hurt and killed by getting sucked into the filter's intake. If you search for "Hydro Sponge Filter" these are super to use to cover the intake line. Besides keeping your small fish safe from getting hurt, they work wonderfully as a pre-filter to keep the media in the canister from getting clogged up with algae and debris. It's much easier to turn off the pump, remove the hydro sponge pre-filter and wash it, etc. Not needing to take the canister apart to clean frequently not only saves time and mess, it leaves the beneficial bacterial inside the canister undisturbed. Using a Hrdro Sponge as a pre-filter for the canister filter will provide additional surface area for beneficial bacteria as well. This helps keep your water quality good, especially if you are like many of us who sometimes overstock our tank or feed too frequently. If you enjoying tinkering and want to try a larger and/or additional pump with this canister, don't put it on the intake, as this can result in too much pressure in the canister resulting in leaks. Its pump is on the canister's outflow so it doesn't cause pressure in the canister that results in leaks. Before I ordered my second one of these SunSun filters, I first tried an additional pump to increase flow using a really strong a power head I already had and wasn't using. I put it inside the tank on the end of the return line. It worked well, but I finally decided I wanted the second filter with slower flow rates instead of one filter with a really high flow rate. The bigger pump kept the water quality good, but the water turbulence was excessive and messing with plants and stuff.
