Keeping the balance: feeding, pH, temperature

Students will

• Explain how the amount of fish food sets how much plant food a system makes.
• Explain why leftover fish food is a problem.
• Explain why aquaponics growers aim for a pH near 7, a middle point for fish, plants, and bacteria.
• Describe why growers change one thing at a time.

Talk about it

Think of something you keep in balance, like a fish bowl, a pet's food, or your own sleep. What happens when it tips one way?

Check questions and answers

1. You feed the fish much more than they can eat. What happens?

   • Leftover food rots and makes ammonia (answer) Right. Rotting food adds ammonia, and too much ammonia stresses the fish.
   • The plants grow twice as fast Not quite. Food that rots makes ammonia, not faster plants.
   • Nothing, because the fish save it for later Not quite. Fish don't save food. Leftovers rot in the water.

2. Why do aquaponics systems run at a higher pH than hydroponics?

   • The fish and the crew like it higher (answer) Right. Plants like it a bit sour, so growers meet in the middle, near 7.
   • Plants like a higher pH in aquaponics Not quite. Plants still like it a bit sour. The fish and the crew pull it up.
   • A higher pH makes the water warmer Not quite. pH and temperature are two different things.

3. The fish are calm, but the plants look hungry. What could help?

   • Feed the fish a little more, slowly (answer) Right. More food means more waste for the crew to turn into plant food. Go slowly and watch.
   • Stop feeding the fish Not quite. Less fish food means even less plant food.
   • Add lots of extra food at once Not quite. A big jump makes more waste than the crew can handle.