Potassium in Aquaponics
Potassium in Aquaponics: N-P-K
Potassium is hands down the most interesting and frustrating nutrient to manage in aquaponic systems.
When there is a nutrient deficiency in aquaponic systems, 9 times out of 10, it is a potassium deficiency.
Not only is there typically a lack of adequate levels of potassium in fish feed and waste, but potassium has a rather complicated relationship with other nutrients in the system.
For this reason, I’m going to cover the topic of potassium in a series of several posts, including:
1. An Introduction to Potassium
2. Potassium In Your System
3. Potassium Deficiencies- Recognizing Them and Why they Occur
4. How to Treat Potassium Deficiencies and How to Manage Potassium to Prevent Deficiencies
An Introduction to Potassium
Potassium is introduced to your system in the form of fish feed or supplements like Potassium Hydroxide, or Kelp Meal Concentrate.
Unlike many other plant nutrients, Potassium does not occur at high enough levels in most fish feed to supply adequate amounts of potassium to both your fish and your plants. This means that potassium is often deficient in aquaponic plants (if potassium isn’t supplemented).
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Potassium in Aquaponics
Potassium is a fairly simple, soluble element in your system.
Because it’s simple, soluble and charged, potassium is an important signaling ion, as well as a very simple and effective ion to control the osmotic potential of plant cells.
Basically, the plant uses tiny pumps to move potassium from one area to the next in order to “inflate” those cells with water. Water moves from the cell with low potassium concentrations to the cells with higher concentrations. This allows the plant to keep it’s tissues full of water, which is important since plants are mostly made of water.
It also allows the plant to do things like open tiny ports in the surface of the leaves (called stomates or stomata) to allow gas to enter and leave the plant leaves. It’s also a signaling molecule, meaning that the plant uses potassium to communicate between the different cells and parts of the plant. This helps plants grow and reproduce effectively, as well as mount defenses to diseases and pests.
Potassium deficient plants are more susceptible to pests.
Last but not least, potassium is also very important to the protein making process, and without proteins, plants cannot survive.
Fish also need potassium, and it’s typically in the top 10 most important elements (by % of bodyweight) for growing fish. For this reason, fish feed usually contains quite a bit of potassium.
Unfortunately for aquaponic growers, feed is formulated to be efficient- which means not including much more potassium than is necessary for the fish. In traditional aquaculture, in the best case scenario, excess potassium in the feed just goes to waste.
In the worst case scenario it can lead to other problems in the system. This means that when traditional aquaculture feeds are used in aquaponics, there just isn’t usually enough potassium to go around. For this reason, potassium must almost always be supplemented in aquaponic systems- which brings us to the heart of the matter. . .