So we have removed 5 grow beds. The Big system and tower system are tied together to utilize the filtration in the towers. There is still quite a bit of gravel online but we are working hard to remove the shells and get the pH/water chemistry into better order.
So after two years of heavy filtration the beds are not clogged and just have a healthy amount of worm castings breaking down in them.
Lots of worms in that media. Too bad the shells just mess with the chemistry too much. Shells or limestone or anything else with excess calcium carbonate just doesn’t work well as media for aquaponics.