I am a Special K addict (Why I love Potassium ;)

No I am not hooked on the drug “K”.  But K on the periodic table, or Potassium.

My Potassium love affair started in my old high tech tank in the pre- YouTube era.    I was running mega high lights, full CO2 and dirt out of the wazzo.   (This was my first dirted tank too, so I still had that fresh, “Oh my god- look at how these plants are growing!” feeling. I still get that rush with a newly planted tank, but nothing beats your first time right?)

Anyways- I was dosing the heck out of everything I could get my hands on. “More more more” was the motto for this tank. I have always enjoyed pushing a planted tank as hard as I can on occasion to see what would happen. (this does bite me in the ass periodically though…)

Potassium was one such fertilizer that I never had to really worry about over doing without ill affects.


(ask me how many red cherry shrimp I killed in my tank when I was first testing out my new Potassium Fertilizer)

I found that Potassium made my plants grow larger and fuller.  I was constantly getting leaves where the edges were crappy looking. They looked the plant just ran out of energy to push the food to the ends of the leaves.   (When leaves look like this, it is typically best to just remove them entirely and let new, completed growth come on)

When I started pounding the potassium, I noticed better “Veins” in my plants looked better.

So what does Potassium do in our aquarium plants?

Here is the best way I can explain it in simple terms.


Potassium helps activate over 60 enzymes that play a roll in the plants chemical reactions.  Basically, Potassium makes it easier on the molecules to come together for the chemical reaction in plant growth.

If you want to think of it like a saltwater tank….

In a saltwater tank you need your salinity, or amount of salt to be a certain amount for fish and corals to live. Think of potassium’s role like this only in the cell of the plant. Potassium helps the cells regulate the amount of water in the cells to keep it at a stable ph internally of around 7, the optimal PH for plant growth.

Potassium is also involved in every major step of protein synthesis and stomal activity in the plant.

Potassium plays a pretty critical role in photosynthesis.  When light hits a plant as energy to combine CO2 and water to form sugars, the first energy product is called adenosine triphosphate or simply ATP.   The electrical charge balance at the site of ATP is maintained with Potassium ions.  Photosynthesis is slowed down when there is a lack of Potassium available.


I have a dear Fish Tank Friend who lives over in the UK and is his degree in Molecular Biology.  He also, shockingly, keeps a mean Aquarium.

Daniel Clegg says….

“Okay so I’ve got some key points that should be useful to pull people in and if they wanted some high level molecular biology I can go more in depth but basically:

To understand the use of potassium imagine that a plant leaf is made up of lots of little water balloons, this is pretty much what a section of leaf looks like under the microscope. Potassium controls the amount of water that is in these balloons, making the leaf look thicker and healthier. Potassium also controls the uptake of other nutrients into the plant. The best way to understand this is imagine for each nutrient to pass into the plant they need to enter by a toll road and the plant uses potassium to pay the toll. Another use for potassium that most people aren’t aware of is to produce carotenoids which are the pigments which turn plants red.

When plants are low in potassium you see dead spots ( the little balloons don’t have enough water and dry out and die ) you also see yellowing as the chemical reactions that are being carried out in the leaf become unstable and sugars begin to oxidise ( same reason an apple turns brown if you cut it and leave it.)

Thank you Daniel! (and yes- he is a member and will be contributing more

Let me put this in simpler terms-  Pour a little of this stuff on to your plants and watch closely as they perk up and probably send off a bubble or two.  You can see this in a video a did here (I dump it in at 2:10) Notice the bubbles coming up after?

Other comments about Potassium…

I have found that Potassium has greatly reduced the melting back of Jungle val in my greenhouse tanks.   I have also been able to keep the leaves on my Madagascar Lace plants from falling off when I am consistent with my Potassium dosing on those tanks.

As my general routine,  when I get new plants in, I add about 3 table spoons (the big spoons)  of my Potassium to each of my 125’s.  This makes for significantly less melt off in the plants.

I have found that Potassium is often the “Limiting Factor” in my tanks. (third under good light and CO2 in the case of the greenhouse tanks)   When you run high levels of potassium, you might see different looking deficiencies in you plants. Here is a great article to pin point those.


And yes- I do sell my own Potassium Fertilizer here. (which will last a 30 gallon tank a year!) Click here.