the gravel, a 300mm layer of cardboard form the local supermarket, then a good garden mix soil (Pauls secret herbs and spices lol) and a final layer of good quality mulch.  Took some hands and a bit of machinery to get all of that in. Now it gets a little tricky.  The fish tank has a liner inside that green aquaplate ring and it has a sump underwater in the centre.  That is how we get to gravity feed.  The three large pipes have pipes inside them.... and act as a level control for the tank.  They are the outlet by gravity to the garden beds. The water flows through the garden beds and back to that centre drum (sump) in the middle of the tank which is in the ground a fair way.  The sump in the middle is where we pump the water back up into the fish tank and around it goes. We attach a spray bar for some aeration across the top and connect a 12 volt inline water pump (ready for solar) to get the water moving.  Great to stick with 12 volt around water, electrics and children (or adults for that matter). There are about 200 gold fish to start out.  As much as I am not the goldfish biggest fan, the kids love the colours and it gets them interested.  We may change out to a native species another day... A bit of mulch to pack around the  fish tank to keep the