Marine pure is good. There are several brands of bio blocks which come in balls, cubes slabs, and bricks from Brightwell Xport bricks.
I have Marine pure but the bricks look interesting because they will stand up and allow water to pass by because of the dimples /spots holding them above each other.
They all have data showing how and why theirs is good/ or better than the other.
I didn't use my sump but when I was going to set it up the water flowing in is set to go into a filter sock like with a saltwater tank.
You use a filter sock mount or holder and it attaches to the side of the sump catching the larger mucky stuff. This you change pretty regularly every few days, it does depend on the amounts of fish and foods you use, and having an extra or 2 is a good idea said my friend since you can swap it out in a quick minute. You can rinse them out but eventually need to replace them. Though they aren't that expensive.
The order of filtering is
mechanical,
biological
chemical
I will send you a link in a PM. They show the sump using K1 media which I have always wanted to try, it has a commercial advertising connected to it so I am not posting it to the thread.
