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.Oh 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.