Potassium in the Reef Tank & K Test Kit




Despite it being a major element of natural sea water, as an element in our reef tanks, Potassium (K), is often overlooked. From what I’ve read in articles and discussions, regular water changes should be sufficient enough to keep it moderately maintained, albeit less than NSW levels of K. And, I’m not sure whether it is an aspect of our reef chemistry that needs to be focused on maintaining, unlike the ever important calcium, alkalinity & magnesium. It does seem to be more a focus in aquariums running low nutrient systems, as there are reports of STN & other issues in zeo tanks experience low levels of K (Scroll down a bit on this thread to read G. Alexander’s description of a potassium leak in his tank).

Considering I strive to keep other players within NSW ranges, I decided to try and start maintaining NSW levels of potassium (~380) to see if there is any noticeable effect on my tank. So, in order to better approach the situation, I grabbed a K additive and Fauna Marin’s Potassium (Kalium) test kit to see where my K levels might be…

I’m interested to see if it does make a difference, or if it turns out to be one of those additions like Strontium or Iodine, with which I do notice some effect, but not enough for me to care about it. If it does or not, I can at least add this to my list of tests to compare vs. results from AWT…

Here’s the contents of the kit.

If you’ve used DD Merck’s Phosphate kit before, this is similar in terms of number of steps. I think the Kalium test takes one or two more steps, but about the same amount of time, and instead of comparing colors in 2 different tubes, you’re comparing the turbidity…

The first step is to draw from the 250ml bottle of distilled water.
Add 7ml into each of the short glass tubes.


Provided in the kit is the ‘K-referenz‘ - the turbidity of this solution is what you will match the turbidity of your aquarium water with to get a reading. Now, since I have no previous knowledge of what my K level in my tank is, I’m using a known standard in place of it - FM’s Multi-Reference solution.

The multi-reference solution is calibrated to 415 mg/l Calcium, 1295 mg/l Magnesium, 395 mg/l Potassium, 3 mg/l Silicates, 6.6 dkH & and a Salinity of 35ppm. Thus far, it’s tested at exactly the levels stated for Ca - kH - Mg and salinity, so I don’t really have any reason to doubt the K value is 395. So next step, using the green syringe…

1 ml of the K-referenz and 1 ml of the water to test into their respective tubes


Then into each tube, 8 drops of the reagent


Shake ‘em up, wait 3 minutes


Now, using the white syringe, take 3ml of the mixed solution (w/ K-referenz) and add to a tall tube. Then take only 1ml of the other solution (the one you’re testing) and put it in the other tube.

3 ml reference (left), 1 ml water to test…


Now to compare the turbidity. With my eyes and the nature of this test, I am glad I used the known standard…. Here’s the initial view - 3mL of K-referenz on left, 1ml of water to test on right.

Notice the black cross. It is a bit sharper on the right.


Drawing another white syringe full (1 mL) of the test water, I add to the tube drop by drop, trying to eyeball the shifts in turbidity for a few seconds after each drop. Ended up adding the whole 1ml of the syringe. After scrutinizing the results in different light for 5 minutes, I determined that the tubes look exactly the same (the light in the photo skews what I saw a little, but they’re the same).

Black cross in each tube looking down appears to have the same ‘blur’.


But just to be sure I was reading the turbidity correctly, I drew another 1ml of the water, and added it to the tube… the one on the right definitely got more ‘blurry’ with each drop, so I assumed the 1st endpoint I suspected was correct…

Hard to tell in the photo, but right side is past ‘endpoint’…


I look at the instructions and calculate my first reading. To find K level, take the number of syringes completely emptied (2, in my case), add “1″, and subtract the number of the remaining quantity in the syringe (’zero’ in my test).

2+1 is my number.


According to the chart, reading consumption (#syringes +1 ) on the bottom axis, and following straight up from the reading, I’m pleased to note that a) my eyes were good enough to see a decent match, and b) the multi-reference solution was right on the money ~400 mg/l Potassium. Now, to test my own aquarium water…