I thought I would move this discussion here as we threadjacked dennis's thread.
I can only to speak to my reasoning for lowering K. In the past, I was raising the KH of my RO water to about 4 dKH. Using K2CO3 that meant a lot of K....50+ ppm.
I don't understand why the calculators (Rotala and Zorfox's) are stating Potassium in ppm is the same between KHCO3 and K2CO3 something I am missing but you should have half the potassium for the same carbonate so I'd use Potassium Bicarbonate if you could find it over Potassium Bicarbonate for sure.
However my preference if I ever do RODI is to to go to a Kh=3 and live with 25ppm of Sodium. Not sure why you don't want that level of Sodium in your tank?
Why kh=3? well S. Repens for one are stated to need a minnimum hardness and I wonder about other species. Plus for Shrimp and Snails the pH range seems a lot safer for them. I'd rather not go below ph=6.5.
I tried many times to lower NO3 & PO4, as I just thought it should work. It never did.
That is a mouthful right there and looking at the chart at one point you had phosphate up to 18ppm!
According to Mulder's chart K inhibits NO3 and PO4 so its possible that is/was the problem.
Then I was having a discussion with Joe, and he mentioned that he had been speaking with Vin Kutty about a guy from Germany who keeps all his tanks with K lower than Mg with great success. So I said what the heck, I've gone this far, might as well jump further down the Rabbit hole.
That is funny, "I know a guy who knows a guy who knows a guy from Germany who keeps K lower than Mg with great success"
Why K lower than Mg I don't get the relationship? (How high are Ca, Mg and K though?)
So then I started slowly lowering my KH and total K even further. KH now is just about 1 or so, and I am using MgNO3 instead of KNO3.
Calcium Nitrate is readily available here maybe I'll use it in the future. I get what you are trying to do if you refuse to use Sodiam Bicarb.
So I REALLY lowered my K. At the same time I began lowering everything else in proportion, including micros. I figured the worst thing that could happen was going back to my old dosing scheme, which I was all in all I was pretty happy with.
Biggest problem is it could take months before your plants really show deficiencies and by that time you probably have changed many things (added/removed plants) many other problems.
So far it has worked out very well. Biggest difference is nuisance algae like GDA on the glass is totally gone. I'm still paying very close attention to see if any deficiencies pop up, like what happened to Joe.
I found the same thing as soon as I lowered my dosage GDA was reduced immediately. Dennis has talked about this on his website as well.
I was so nice to be in Tom's world were excess of everything had no negative effects but that was a bit of "ignorance is bliss".
Also shows that the system can withstand some pretty wide swings in dosing yet somehow manage to do OK.
Once plants are healthy and robust they can have stores of nutrients saved up, they can be pretty resilient that is why it may take a lot longer to see deficiencies in some case. I guess countering that is you guys use such strong light so you are driving growth so fast those stores are depleted more quickly.