[Laith]

I posted this on the APD and thought it could be of interest here too.

I think that K uptake by plants might be higher than we think. I've been dosing it regularly through KNO3 and/or K2SO4 so that at water change I'm adding 20mg/l. And then mid-week adding 4-5mg/l.

I've always wondered what the actual levels and uptake was so I finally broke down and bought a LaMotte K test kit (ok, so I'm a control freak! ). I received it mid-week and I did the first test 3 days after water change and dosing (and before my usual mid-week dosing). The result: 8-10mg/l of K. Which logically means that I was at 0 when I did my water change!

I dosed 10mg/l of K at that point. 2 days later I measured 14-15mg/l of K in the tank. So an uptake of 4-5mg/l in two days.

Given that K is the nutrient that the majority of us never measure (we just dose to a certain level), could it be that more problems than we realize are due to a deficiency in K? and this causes an imbalance or uptake problem of other nutrients? :?

 

[bharada]

Both my tanks have pretty large fish loads (in part due to a Guppy population explosion!) and were showing signs of K deficiency--pinholes in older leaves. So now I add double the ppm of whatever I dose in KNO3. So when I dose 5ppm of KNO3 I add 10ppm of K (via K2SO4) just to follow the 2:1 K:N ratio that's been indirectly recommended in the past (i.e., 20ppm K : 10ppm NO3).

 

[plantbrain]

You will want to measure NO3 as well.
See if the levels are related.

NO3 can have 3-5ppm per day usage, 2-3ppm of K seems a little high to me. The other issue is that both kits are tough to read making more precise ppm hard ot read.


Regards,
Tom Barr

 

[gregwatson]

I tell everyone who asks that I don't personally subscribe to much of the "current thinking" that has leaned towards dosing less and less Potassium ...

I continue to dose twice as much potassium sulfate as I dose potassium nitrate ...

A wise man once told me that "your plants may appear to be fine to you, but how much better might they have been if you had dosed xyz" ...

So while much of current thinking leans towards dosing less potassium - most of current thinking suggests that high potassium levels to not contribute to algae ... thus I continue to dose higher levels of Potassium until a "wise man" like Plantbrain up above gives me a scientific reason not to <grin>!!!!

Greg

 

[Edward]

I have experienced higher NO3 uptake with extra K2SO4.

 

[JLudwig]

NO3 can have 3-5ppm per day usage, 2-3ppm of K seems a little high to me.

I have LaMotte NO3 test kit, plenty of CO2 measured with a pinpoint probe and LaMotte alkalinity test, plenty of PO4/K, 7 watts per gallon and I have never ever seen uptake rates much larger to 2ppm NO3 a day. Not that tanks don't run better at 20-30ppm NO3, cheap test kits might have you believe something different tho...

J

 

[Laith]

Yes, I don't think I've ever seen uptakes of NO3 in my tank of more that 1, max 2 per day. On the other hand, it's difficult to tell how much the bioload is adding per day too.

Now that I'm dosing higher K than previously, I will see if the NO3 uptake increases.

I was always puzzled why I was still getting pinholes in some older leaves when I was dosing around 25mg/l of K per week: they were the reason I started dosing K. Can't wait to see if the holes disappear with higher dosing...

 

[aviel]

I think I had the same problem here,

My tank nitrate uptake rate slowed down and I just couldn't figure out why. Plants growth as well as pearling was slowing down. I of course added smaller and smalller amounts of KNO3 until the tank was almost stunted. At that point I had this revelation like the one Jesus was experiencing 2000 years ago... - The K uptake was a bit higher than N uptake so by adding less and less KNO3 I made my tank K limited. I dosed ~10ppm K from K2SO4 and when I came home the night after - the tank had a serious pearling explosion. And of course - Lamotte K test kit is supposed to be now on the plane to the holy land.

Aviel.