Sorry about that. There is a product, I'm not sure which brand, that is a solution of zinc sulphate that you add to water, and you can taste test that. For potassium, I use the Morton Salt Substitute and add 1/4 tsp to about 32
oz of water. I taste that. If you can taste it, then you are likely not low, but if you can't, you may need a bit of K. I must say that for the zinc, this is a tried and true method. For the potassium, it is just something that I stumbled upon, and it may not hold true for all. However, I will say that the body is believed to need quite a bit more than is thought to be consumed in a standard diet, so additional K (if a person doesn't have a condition that contradicts it) can be beneficial to most.
As to the signs of mineral need, my skin conditions were my first clue. When I began investigating supplements it occurred to me that any imperfection of my body was likely linked to my nutritional status. Skin blemishes, vision problems, intestinal issues, heart beats, even cellulite. So far, I have improved my vision from 20/100 to about 20/40 in my strongest eye, I have cleared, with some consistency, a 20+ years bout with
Acne and severe dry skin, and I have lost almost all signs of cellulite(this mostly from dropping gluten/dairy from my diet). My physical responses to minerals/vitamins are often in the form of increases/reductions of inflammatory skin reactions and dryness. The best clue I got to what might be causing my issues came from acu-cell.com. That is where I learned of the side specific aspect of minerals. It also helped me isolate which nutrient might be causing my problem. Without a trained naturopath in my area, I had to use a bit of trial and error, but it has paid off for me. I now understand what is triggering my reactions, why it is affecting me, and what I can do to counter it. Example: I drink a large citrus drink, and the next day develop a painful cystic bump on my face or back. I know that I'm sensitive to citrus fruits, but instead of thinking that I'm allergic and avoiding them like the plague, I realize that my reaction is due to my low zinc/copper status being aggravated by the vitamin C in the fruit juice. So, I supplement either mineral, depending on which side reacts, and by the next day, the reaction has cleared. Or, I realize that I have been consuming some pretty acidic forming foods lately, and that I haven't had much calcium-rich foods. So, I supplement my calcium, and my skin clears, again by the next day. For me, my response time to the correct mineral is very fast. Even long-term problems like the severe dry skin was cleared within a week. I had major peeling, like I was shedding my body for about 3 days, then after a shower, simply rubbed my body with my bare hands while I was still a little moist, and the dead skin just rolled up and fell off. It was beautiful! Also, since I have been trying to increase my stores of the most deficient minerals, I don't have as frequent or severe reactions to foods or things that might have thrown me completely off a few months ago.
For me, the stool changes have helped me most with balancing my calcium with my magnesium. It was a tool I learned to use while doing liver flushes. But, recently it also clued me in to my zinc balance. When zinc is low, it can cause diarrhea/soft stools, too. Zinc moves vitamin A out of the liver for usage by the body, and when zinc is low, I believe it can affect the intestinal issues that benefit from A. This also may be what has helped my vision so much.
Also, for the past several years I have experienced heart palpitations. I thought that I would be stuck with them. But, now that I have improved my mineral status, I seldom have a palpitation, and when I do, I'm learning to distinguish what is awry. High calcium usually means a strong fast beat, while high mag means a fast beat, and what I normally consider a palpitation. Of course, the electrolytes can have an effect, but I haven't figured out which is doing what there. I just play it safe a drink a Propel if I think my electrolytes may have gone low.
But, the body reactions are definitely personal. Some people have major joint reactions or muscle cramps, others develop eye infections or skin rashes. So, you will have to figure out how each mineral's deficiency affects you.
Good luck, and let me know what works for you.