Tuesday, 29 October 2013

Nutritional Supplements For Aquaponics

This topic is covered in more depth on our online workshop.

Fish feed and consequently fish waste supplies most of the nutrients required by plants in adequate quantities. There are some deficiencies however that often must be addressed by adding supplements. Here is a table of the nutrients required by plants:

Most Systems Require Calcium, Potassium and Iron Supplement

The 3 nutrients that must usually be added are Potassium, Calcium and Iron. Sometimes a little Magnesium and Phosphorus are also required. Since the pH in a well functioning system should always drop over time (due to the nitrification of ammonia), the best way to adjust the pH and add nutrients at the same time is to alternate between Potassium Hydroxide and Calcium Hydroxide. (Here is a pH adjusting kit that includes everything you need). This will give you a balanced amount of Calcium and Potassium. Some people prefer Potassium Carbonate and Calcium Carbonate, but the carbonates buffer the pH making it hard to adjust to the desired level accurately. 

To add iron to your system, use chelated iron (DTPE not EDTA). Here is a link to our iron calculator that tells you the UVI recommended amount to add each week (most systems require this much or less).

If you need to lower your pH, use phosphoric acid since your plants can also make use of the phosphorus. You will likely need to supplement phosphorous only for fruiting and flowering nutrient hogs such as tomatoes or cucumbers. If you need to add phosphorous without adjusting pH use rock phosphate

How To Spot Deficiencies

  • Nitrogen: Starts with older leaves becoming more yellow than the younger ones. Entire plant starts to turn yellowish.
  • Calcium: Newer leaves show distorted growth. Mild deficiency can result in cupped or curled leaves and moderate deficiency can result in twisted leaves that look like they're squished.
  • Potassium: Older leaves start to have small dead areas that start like little pinpoints and grow. Yellow areas can appear which then wither at the edges and tips
  • Iron: Newer leaves show reduced chlorophyll. Leaves turn yellow with greenish nerves enclosing yellow leaf tissue. It's first seen in fast growing plants.
  • Phosphorus: Plants stop growing and become darker green (some species become purple). Premature leave drop-off. Fruiting plants such as tomatoes are not producing.
  • Magnesium: Older leaves start to yellow from the edges inward. The midrib may remain green while edges are yellowed or whitish. (If you need to add magnesium you can use epsom salt)
Graphic From GrowREALFood.com

pH Affects Nutrient Concentrations

Be aware that the pH levels in your system will affect the nutrient availability in your system. Try to keep your system between 6.4 and 6.8 pH.

For more in depth information on each nutrient and how to spot deficiencies click here ...

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