Potassium and algae / macroalgae

[Cory]

I have a waterfall ats and some caulerpa racemosa. Potassium before was testing at 380 ppm via salifert. Po4 was .22ppm via hanna checker. I decided to raise my potassium from 380 to 410ppm. To my surprise, the macoalgae and waterfall ats increased its growth a lot! Previously the ats would have yellow dead growth under the first 1/2". Now after the harvest it was 1" of growth and green to the bottom with no dead growth. And the caulerpa is nearly doubling in size every 5 days. Is potassium boost of 30ppm really the reason for the growth increase?

 

[Dan_P]

I have a waterfall ats and some caulerpa racemosa. Potassium before was testing at 380 ppm via salifert. Po4 was .22ppm via hanna checker. I decided to raise my potassium from 380 to 410ppm. To my surprise, the macoalgae and waterfall ats increased its growth a lot! Previously the ats would have yellow dead growth under the first 1/2". Now after the harvest it was 1" of growth and green to the bottom with no dead growth. And the caulerpa is nearly doubling in size every 5 days. Is potassium boost of 30ppm really the reason for the growth increase?

Put me down as a doubter that a 10% change was important. By the way, how did you increase the potassium.

 

[Cory]

Put me down as a doubter that a 10% change was important. By the way, how did you increase the potassium.

I used brightwell potassion-p. All at once mixed into ro water. Iirc it was about 32 grams potassium into 150 ish gallons tank water.

 

[Dan_P]

I used brightwell potassion-p. All at once mixed into ro water. Iirc it was about 32 grams potassium into 150 ish gallons tank water.

Got it.

Any other dosing changes?

 

[Cory]

Got it.

Any other dosing changes?

I dose iron citrate. I also made a new batch. Perhaps the new batch was more bioavailable than the old batch. The old batch was a year old.

 

[Cory]

It seems im not the only one who noticed this:

PS in low levels of potassium I notice slow to very slow, growth of chaeto in refugium and algae on ATS.....but the point here , is high levels of potassium

Perhaps my test kit isnt reading the correct potassium level and is actually lower?

 

[Dan_P]

I dose iron citrate. I also made a new batch. Perhaps the new batch was more bioavailable than the old batch. The old batch was a year old.

This seems more like an explanation than a 10% increase in potassium.

 

[Dan_P]

It seems im not the only one who noticed this:



Perhaps my test kit isnt reading the correct potassium level and is actually lower?

Something to consider. I wonder if @Rick Mathew has any ideas about the potassium test?

 

[Randy Holmes-Farley Verified Community Expert]

If we think about limiting nutrients for growth, then as we add enough of a presently limiting nutrient to eliminate that particular limitation, we move up the list to the next limiting nutrient.

At some point we might get to potassium before we shift to nonchemical factors, such as light or temperature.

Eventually, things are growing as fast as biochemistry will allow, no matter what else we change.

Where does potassium in seawater fit into that scheme? I have no idea, except it’s not among the first things that limit growth (N, P, Fe, etc).

I agree I’m skeptical that potassium caused the change here.

 

[Cory]

If we think about limiting nutrients for growth, then as we add enough of a presently limiting nutrient to eliminate that particular limitation, we move up the list to the next limiting nutrient.

At some point we might get to potassium before we shift to nonchemical factors, such as light or temperature.

Eventually, things are growing as fast as biochemistry will allow, no matter what else we change.

Where does potassium in seawater fit into that scheme? I have no idea, except it’s not among the first things that limit growth (N, P, Fe, etc).

I agree I’m skeptical that potassium caused the change here.

The salifert potassium test kit is almost expired. I wonder how reliable they are near the expiry date? Could i make a diy potassium and sodium chloride reference check to verify its accuracy?

 

[Randy Holmes-Farley Verified Community Expert]

The salifert potassium test kit is almost expired. I wonder how reliable they are near the expiry date? Could i make a diy potassium and sodium chloride reference check to verify its accuracy?

Yes, but a better way (since the matrix may mater substantially for accuracy) may be to take artificial seawater near 400 ppm (most are) and add 100 ppm of potassium and see if you get the right boost.

 

[Cory]

Heres my results:

35ppt instant ocean tested at 370ppm K.

Added .1g of brightwells potassion-p to the 420ml of saltwater i made and got 460ppm potassium. Seems okay?

Salifert potassium test kit is a drop by drop test from a squeeze bottle so it isnt very precise.

I used the planted tank calculator for potassium sulfate. Brightwells potassium supplement is probably mostly potassium chlordie so im not sure the weight difference.



How i made my artificial seawater:

400ml of ro water
16.98 g of instant ocean salt

Measurement with my tropic marin floating hydrometer was 1.0268. Close enough.

 

[Cory]

What if i do an experiment where i add 10g of wet caulerpa racemosa into a cup and another 10g into another cup with the same nutrients, except potassium is higher in one cup than the other. Ill use the same led light above them and weigh their wet weight after 5 days. Could this prove anything?

 

[Rick Mathew]

It seems im not the only one who noticed this:



Perhaps my test kit isnt reading the correct potassium level and is actually lower?

I have been using the Salifert Potassium Test kit for several years. I have not done an accuracy analysis of the kit but I have tracked it in relationship to ICP test results. I have found that the Salifert results that I measure are generally lower by 40-60 ppm ( All of the vendors had better than moderate precision in measuring potassium according to our study...see chart below)

I shoot for a measured value above 400ppm using the Salifert test

Hope this helps

 

[Cory]

I have been using the Salifert Potassium Test kit for several years. I have not done an accuracy analysis of the kit but I have tracked it in relationship to ICP test results. I have found that the Salifert results that I measure are generally lower by 40-60 ppm ( All of the vendors had better than moderate precision in measuring potassium according to our study...see chart below)

I shoot for a measured value above 400ppm using the Salifert test

Hope this helps

I will keep my potassium between 400-420ppm thanks for the info.