High K blocks Ca uptake?

[PeterGwee]

Was browsing through the mailing list and it mention that high K level blocks Ca uptake. Is that true? Anybody using Ca test kit and found out what is the Ca level of Singapore's tap water?

[David]

hi peter....where did you find the article?...this is interesting

[PeterGwee]

Well..sorry David...guess I did not read properly...it is the ratio between K:Ca that gets out of proportion...Singapore water low calcium content I think. The following is the extracted part from the APD mailing list.

>> In that
>> regard, is KNO3 a good source of N and K, because it provides N and K in
>> the ratio 14:39 (~1:3). I dont like to overdose K in soft water.
>

>?? What do you consider overdosing? Interference with Ca uptake? Folks in
>the bay area have soft water and I deal with tanks there and they have no
>problems with 30ppm or so. Certainly nothing that would appear as a Ca issue
>that I can tell. I don't go over 50ppm but a 40ppm has been added and Im
>sure abuses go on but we hear little horror stories of K
>overdosing...........and that's a good thing


Yes, I was thinking about interference with Ca uptake. There is soft water
and very soft water. If you or other people in bay area are carefully
adding/replenishing their Ca and, lets say, keeping 4<GH<6, then 50ppm K
wont be a problem. But if (1)Ca addition is not part of your normal routine
and you have very soft water (my tap water has 10ppm Ca and if I dont keep
up, it definitely goes down from there) and (2) you are regularly adding
KNO3, then the K:Ca ratio can get out of whack. I noticed that among my 3
largest higher light/faster growing tanks, that one was doing poorly. This
was one that got the most additions of inorganic macros. After finally
testing for K, I found it had 50ppm K whereas the good tanks had 20-30ppm.
After doing major water changes, the poor tank improved.... but it took
months for the plants to show it. Of course, water changes correct MANY
problems, but this is one piece of anecdotal evidence that made me concerned.

BTW, in natural waters, there is 5-10x more Ca than K
But, when I check critical conc ratios and nutrient solutions like
Hoaglands, there is 2-3 more K than Ca. So...????....... maybe high K is
only an issue when K:Ca ratio is really out of whack?