The aquarium you see in my profile picture is a 20gal (roughly 78 liters) tank kit that was from Tetra brand. It included a Tetra EX20 filter (which is incredibly silent running), a filter cartridge, samples of various Tetra products, and the local fish store even threw in about $30 of various plastic plants free of charge (later found out that they did that because it was older stock they were trying to get rid of. Still great looking artificial plants though!). My whole starter kit, not including the heater (purchased separately) was on sale for $55.
To start, I had set up the system as is but really wasn't happy with the default equipment the tank came with. Not long after setting it up, I bought an AquarClear 50 HOB
filter, fluorescent light bulbs for my hood, and a lot of custom filter pads/sponges and bio media. After setting up my AC50 with the custom filter sponges, I then decided to customize my Tetra EX20 with those same filter sponges and a bag of bio media. The Tetra EX series of filters come with a biological unit known as the "bio scrubber" that sits in front of the filter cartridge. It can be removed thankfully and in my opinion it was just awful at establishing a beneficial bacteria colony. Combine that with cartridges Tetra wants you to throw away every 3 weeks or so and you are set for a disaster (mini cycle) in your tank. Now that my Tetra EX20 is fully customized I never have to worry about a lack of beneficial bacteria coming from that filter thanks to the bio media plus now I have various sized filter sponges occupying the space where the cartridge would go. No more changing things out every 3 weeks and spending a lot of money on subpar filter cartridges.
My tank has the AC50 on it with the customizable media in the back and is running with the Tetra EX20 now also customized with my own media. My water has never looked better and my water parameters are perfect!
I would also recommend adding a true bacterial additive to the tank when you first get it set up and then do fishless cycling rather than fish in cycling. You can find tons of info on here about fishless cycling. As for a excellent bacteria additive I strongly recommend using Dr. Tim's One and Only for freshwater tanks (or salt water tanks if that is what you are setting up). Works instantly and he will sometimes send you a free bottle of pure ammonia with your order so you can get right into your fishless cycling phase.