Don't worry, the first year or so of fishkeeping is a steep learning curve! There's so much to learn, it can feel overwhelming at times! You'll pick it up. @essjay is right, those filters that have cartridges are a bit of a con. Not really helpful to remove and replace media, and it gets expensive! Once people have been in the hobby for a while, they quickly learn how to modify filters so they work better, and you're not throwing away beneficial bacteria along with your cash. It's in the manufacturers interest for people to have to buy new product from them every month, of course they say to replace it often. They're not gonna tell you that you don't need to run carbon all the time, or that you're better off replacing their media with plain old filter sponges that will last for yearsOh I thought you meant a tetra filter lol. I think thats just a fleck of a leaf or something. No tetras for me. Just Barry. I'm overwhelmed by one fish lol
Also thank you for the filter advice. It's confusing with all of this because the box says to change it every two weeks and I'm just trying to read up as much as I can to decipher what's true. I had no idea it would be this much time and info for one small fish! Oy luckily I can afford it right now.
Have a listen to this video when you get chance. It's pretty long, but Cory goes into detail about 'optimising' filters... replacing media and things just like Essjay and I are saying, including for hang on back filters like yours.