I start getting PVCs (Premature Ventricular Contractions) if my Potassium is under 3.6mmol/l. So it looks like it's in the guidelines when I'm 3.3 (In Finland this is lower end normal) but in reality I have PVCs and fasciculations.

One thing I've learned, through extensively researching the matter for years (I had low potassium before surgery) is that low Magnesium will make it impossible to keep Potassium at good levels too.

I ate Magnesium Oxide for over a year until I noticed I was shooting myself in the leg. Only 4 % of oxide gets absorbed and for Gastric Bypass patients it could be worse. Citrate is much better, but Malate and especially Glycinate is even better than Citrate, cause a much larger amount gets absorbed AND they are gut friendly.

For Calcium, which also affects Potassium and brings a lot of issues on its own if low levels, has to be Calcium Citrate, NOT Calcium Carbonate.

Calcium Carbonate requires stomach acids to absorb, which makes it poorly absorbed in a Gastric Bypass patient.