I don't think you have anything to worry about.

Hey,
I think you are ok, well i am still going so...

Intresting topic though. Espically with the recent boom in the hydroponics industry in the last 15-10 years. Now there is a plethroa of different nutrient companies. And alot pf us blindly trust that each batch is exactly the same,and of high quailty.

I remember advanced nutrients getting flamed for the amount of heavy metals in their jungle juice formula. Some even say Canna use P.G.R in their Canna boost. Infact I think they admit that. Basically thats why all the company feed schedules have a week flush with just water for a week.
I doubt that this week could remove a large dose of anything from a plant.

Infact you can get heavy metal reports for different nutrient lines online. Just takes some searching, google Oregon State test for heavy metals in commerical ferts or similar and you should get that advanced nutrient stuff.

But yeah, i guess the best way to be sure would be to buy raw chemicals on mass and mix them yourself. I dabble in this and find the free hydro buddy program indispensable.

It allows you to use the atomic weights from the chemicals to come to a correct indication on fert ratios. So you can make your own and know there is however much elemental phosphorus as opposed to a standard value. And more importantly know there is no bad stuff in your ferts and plants!

Take it easy.