How to know if I have enough potassium / magnesium / iron / salt in my system. My system seemed to be stabilized with PH running around 7 same as my top up water and amonia and nitrites at zero and nitrates just north of zero. Plants were struggling though until I added some magnesium, potassium and iron so that is cool, however I don't know what are the right amounts, I'm still on the "toss 'e…