I dose 5 mL/month. This equates to adding:

1.6 ppb Iodine
.4 ppb Iron
1 ppb Magnesium
0.08 ppb Manganese
0.01 ppb Molybdenum
1.1 ppb Potassium

Natural sea water levels:
http://tinyurl.com/ynxyql

I am talking about the principle of adding ions to the tank
you cannot measure home so you do not know if they are used
up and need replenishment

So am I. What did you think I was talking about?


, or they are already too much of them.

How do you know you are adding the correct trace elements with your sea
mix?
http://www.aquacraft.net/w0023.html

Not having chemistry lab at home I will never know the levels
of - let's say molibdenum in my water - so I have to assume
that the best composition of ions I can get is in sal****er
freshly made with salt mix. Of course some salts will be better
than others, but without tests I would not risk adding or
removing elements I am unable to test their concentration.

You add elements you are "unable to test their concentration" of every time
you use your salt mix. Don't you?