I had a period of time when I was drinking a lot of salt water. Salt is something that is easy to tell when your body needs it as plain saltwater will taste good. I was probably getting many many times the DV but apparently wasn't storing sodium properly.

I think minerals are important but they are not an end all means to dealing with mercury. Like you have been learning, supplementing minerals is difficult as they interfere with other minerals from being properly absorbed. I personally have tried many mineral supplements and only benefit from magnesium, and occasionally iron as my diet is low in iron.

If you read the work of Weston A Price you will learn that fat soluble vitamins are also crucial to mineral absorption, things like A, D3, K2, etc...many of which are found in butter and things like egg yolks and organ meats.

Also, things like Taurine can help you absorb and retain magnesium better, so you don't have to take as much and you get other benefits from the taurine as well.