I filled the reactors with gfo and carbon from premium aquatics.
I have tried many, many, many products over the years but these are by far my favorites.
Gfo likes a slow tumble at the top, sort of like boiling water. You can use your dc pump to adjust that flow.
It's heavy and does no good if not tumbling. Just becomes a rock.
Carbon is in the second chamber and doesn't matter flow so much.
I tried a Rox carbon last week but like the bulk carbon better.
No promo add here but shout out to
@premiumaquatics for great prices, tremendous service quick turnaround, free shipping and no BS.