These are usually sold in those beginner tank kits you can find in pet stores; they are maintenance free and again inexpensive. You can also make your own DIY under-gravel filter if that tempts you more. You place the filter on the bottom of the tank, under the gravel. Unfortunately, these tend to clog over time, but again it’s relatively maintenance free so you might need to vacuum the bottom of the tank every few weeks to remove any particles to prevent clogs.
