Another option for aquaponics is to go without a medium for the harvest plants. Sheets of styrofoam float on top and plants, usually lettuce or other small leafy greens, are anchored in small mesh pots that fit into holes in the styro sheet. The key to success with that method is keeping the solution sufficiently oxygenated. I would suggest additional airstones or sponge filtration.
Easing my toes in the water