Join Date: Jan 2008
If you are only going to dose once per week, there is no way you will overdose.
Commercial fertilizers are mostly water as well, so there is another layer of "security," if you want to call it that.
If you want to check your levels, just buy a phosphate and nitrate test kit.
Potassium is very difficult to overdose on (and you will run into other problems by that point), so there is no need to test for it.