Richard bray

Corrugated Plastic
Although this material has the most potential for long-term rafts, it is not widely used. Corrugated plastic is exactly like corrugated cardboard; the ends of the material are open to show the fluted material in the middle. In order for the plastic sheet to be buoyant, these ends must be sealed.
Corrugated plastic is also the most expensive option; over twice the cost of EPS foam board.
If the ends are not completely sealed, the air pockets will fill with water and the board will sink. The ends can be sealed with 100% pure silicone (no anti-mold or mildew additives), and added to the system once the silicone is fully cured. You can also melt the ends of the board with a torch. Test a sealed board by submerging it in water and checking for air bubbles.
Frames
In a flood-and-drain system, permanent frames with holes cut into them support the plants. As water drains from the grow bed, the roots will be exposed to open air. If a frame does not cover the majority of the growing area, the roots will be exposed to light, drafts, and possible contaminants. This limits most frame designs to some sort of rigid, waterproof board placed over the grow bed.
144
Materials for building a frame must meet the same requirements as all other plastics within the system. Plastics marked with a 1, 2, 4, and 5 SP1 codes are food-safe and non-toxic for plants and fish. Some plastics with an SPI code of 7 are also safe, but you should do more research before adding it to your system.
Plant Support
Deep-water aquaponic systems use a variety of methods for holding the plants upright in floats or frames:
Pros/Cons Rockwool Netted Pots Growing Media
Durable High Moderate High
Stable High Low Moderate
Porous High Low Moderate
Reusable X X
Estimated Cost per plant (2") $.20-$.50 $.40-$.50 Varies
Pots
The size of the hole you cut into floats and frames will be determined by the plants you want to grow. Short, leafy greens can sit in small pots with relative stability. Tall, top-heavy plants will need larger pots to keep them from tipping over.
145
The pots should be slightly larger than the hole cut into the raft or frame. This will allow the pot to fit snugly without falling through.
Netted pots have slits cut into the sides to allow the roots to grow down towards the water. Many hobby growers make their own out of yogurt containers, plastic cups, and other recycled materials. There are also commercially-available hydroponic netted cups that are more stable, but also more costly.
Pots will be filled with either rockwool, growing media, or both. If seeds are germinated in a rockwool cube, the cube can be directly transplanted into a netted pot. Growing media can be poured around the rockwool to add stability, but this is not necessary for smaller plants.
146