Aquarium Mesh Media Filter Bags - High Flow - with Drawstrings for Activated Carbon - Reusable Fish Tank Charcoal Filter Bag - Aquatic Bags for Fresh or Saltwater Tanks (High Flow 3" x 4" (4 Pack))

I use these to hold my Mosquito Bits, so they fully serve my needs as a reliable and cost effective tool. They're easy to clean and reuse and I have no issues with them. Since they are made of plastic, I try to limit the exposure to UV light and heat from the sun. Good price for these items. I'm just glad I got these (the sturdy kind) and not something like a tissue.

I use this originally just to put stones in for beneficial bacteria but it also came in handy to go on the suction tube on my filter after one of my fish got sucked in.

Smaller then I thought

Thanks for working on a Sunday!

The bag has nice open material unlike some other bags that are so tightly woven that the water doesn't flow through it easily. I believe substrate is an absolute must for all aquariums sizes. These new over the back or internal filters just do not have that option. So I make my own media bags. This fits nicely.