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The aquaponic surface area problem and how to solve it

Surface area is so integral to the engines of the aquaponic system — the microbes — that it deeply affects other functions. There are two things in particular that are directly affected by the amount of surface area.

Nutrient cycling is the conversion of ammonia to nitrates, and is key to plant health. Cycling is powered by nitrifying bacteria. Surface area acts as habitat for those bacteria and can be directly linked to the speed and amount of nutrient cycling that occurs in the system.

When hosting microbes, surface area is called biological surface area, or BSA. BSA is one of the direct benefits of high surface area. Systems with high BSA recover from disturbance better, hold pH better, and respond to feeding faster.

Another direct benefit to surface area is cation exchange capacity (CEC). CEC is the ability of media particles to hold exchangeable cations. (Cations are positively charged atoms in a solution.) Since many of the nutrients that crops need are salts which dissociate in water, cation holding equates to nutrient holding for many nutrients.

surface-area aquaponic mediaGood CEC means less fluctuation in nutrient levels. It can also provide a buffer against acidification. This keeps pH from dipping quickly.

Surface area affects the aquaponic system indirectly as well. Surface area has an inverse relationship to particle size; the larger the particle, the less surface area. The smaller the particle, the higher the surface area.

The problem is that both large particles and small particles have benefits and challenges.

Large particles like hydroton are easier to move and plant with, easier to keep clean, and have great water movement. The pore space between particles is so large that solids rarely gather and cause blockage or anaerobic zones.

Small particles offer much higher BSA and CEC, but can be more difficult to work with. Smaller pore space means that solids can accumulate, which can lead to anaerobic decomposition. Sometimes smaller particles can become compacted as well. This introduces a whole new set of issues with planting and maintenance.

Read more at Upstart University
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