If you think it doesnt come from the substrate, it shall come from the
trace mix...

There is literally only a trace of potassium in iron/trace mix.

So lot of it was trapped in the substrate ??
Or is ProFito different ???

I assume ProFito is a substrate material? No substrate should leak
potassium intothe water anything that would is far too unstable
to be ever used in a fishtank.

Okay, now say your tank holds 40 liters. You take out all the water
that you can. About 30 liters. There's still 10L in the substrate.

So, when you add more water all the crap in solution in the water
in the substrate now comes back into the tank water, EVEN IF YOU
REPLACED ALL OF IT. Now, if you have something in yout gravel
that is leaking potassium into the water column that woiuld doit
too. Did you ever use any plant fertilizer tabs in that gravel?


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