Take the steps at work and sneak in some calf raises, when nobody is looking
I do some every day while I’m brushing my teeth because I need to do them for an Achilles’ tendon issue and it’s time when I’m otherwise just standing around not doing anything. (I have one of those fancy toothbrushes that times everything so I just do them alternating legs until the toothbrush stops. Some days I do faster than others, just depends what I feel like.)
I do also make a point of doing some stretches every day on the stairs, also, as you don’t want everything to get too tight - ball of your foot on the edge of a step securely, drop your heel down until you get a comfortable stretch. Just make sure you won’t fall down the stairs if your foot slips. There’s also a rocker gizmo you can get for like $20 that helps do much the same thing, without the falling down the stairs risk.
My personal experience with supplements (just in the context of general exercise, not diving specifically) is it seems to partly depend how much of a sweater you are - the more you sweat the more electrolytes you might be sweating out, and some people do just sweat more/faster than others. So that’s something to keep in mind. That said, a single banana has a pretty decent chunk of the potassium you need daily, so unless you’re losing a lot (like vomiting/GI issues a lot) if you eat some fruits/vegetables every day, an actual potassium supplement may not be necessary. (Some medications do lower your potassium levels, though, so look into that also if you’re on regular meds.)
Also regarding GI issues - some caution is advised with magnesium supplements as they can cause diarrhea in some people/at some doses/in some forms. So definitely not something to try out the first time when you’re about to spend several hours away from a convenient restroom. My mom had to take magnesium supplements and her doctor advised starting with a lower dose (like 1 tablet instead of 2, for example) to see how you tolerated it instead of jumping right to the full dose. I imagine you could probably split it up, too - one tablet in the morning, one at night, maybe - if 2 at a time didn’t agree with you?
Final note: if you do take any medications normally, it’s a good idea to check with your doctor or at least a pharmacist before starting supplements as some things do interact in ways that need to be taken into consideration. (I vaguely remember timing being an issue for my mom, maybe with her thyroid meds and the magnesium?)