The stock media baskets are often bad. Aftermarket media baskets are unnecessary expensive. I went lab and built mine which costs around $10 (for two).
You need Acrylic sheets, I used leftover pieces in the lab. But if you go with the thinnest one, you can get one $5 dollars in Home Depot or Loews. Also need crazy glue (a few dollars) or aquarium safe silicon.
Preferably use a nice thin saw (I used upright bandsaw which made process a lot easy). You need some kind off drill for holes (I used hand drills).
Those are the final products
They fit chamber very nice. I think gap is less then 1/16" for all side so high water flow is guarantee.