Actually, in three years, I've never had a problem with K. I've been testing to see if the old theory "Holes in your plants mean low K. I've never had low K but have had lots of problems with "holes in my plants." In every case the holes were caused by fish predation.
In fact, the absolutest biggest problem I've ever experienced (beside rapid plant growth) was fish predation. When you have rapid fast growing and very tender plants it is surprising what fish will take up vegetarian diets.
I agree, I've never been able to verify that claim myself either.
You could use Ca(NO3)2 in place of KNO3 to do this and test.
That should along with using say Fleet enema for PO4....be able to drive the K+ down fairly low.
Hopefully the tap is K+ free or you use RO.
I've never done it though.
Tasty tender leaves? That's what I'd eat, not the old tough yellow 1/2 dead ones, they have less nutritional value.
Older leaves have more periphyton however, which many species like to nibble on.
IME, poor CO2 causes most of holes etc.
Plants cannibalize themselves to keep growing at the tip in hopes of making it to the surface where there is ample CO2/light. It's a worth while sacrifice.