Just to nitpick. Steel can indeed contain heavy metals but not very often. Usually when you need some-kind of special attribute. The common "mixers" are chromium, vanadium, manganese and molybdenum. Steel is just a general term for a Iron-alloy with 50-99% iron and 0.1-2.5% carbon.
Quite right, in that odd things in small quantities can be found many places. Like radioactive particles in the porcelain items for a foreign ship?
But in general, metal is not really the big bugaboo that it is often painted to be. Rational thinking will show that almost all of our water does already have some iron or other metals in it.
Iron ore is in the ground, in differing amounts all around the country. So are all the heavy metals we fear so much but they are mostly in small enough quantities that they are not a problem even though our water runs through them in the ground. Much more common is the metal that water picks up in our plumbing use. The pumps, pipes, vales and even our own faucets are made of brass, copper and various metals we often call iron or steel.
So the question may be , what do we want to worry about? Do we sweat over using a rock that might look like rust, even though our water has already spent years and years in and around the stuff? In the mining areas like Minnesota, the water is stained rust colored due to the iron ore but then how many fish live in the lakes in the area?
I think I remember folks going fishing in the Boundary Waters area and thinking the fishing was great.
Maybe iron doesn't really kill fish after all?
If you are into raising the really fussy stuff, that is a different situation but one that you have chosen.
Dilution is the solution to pollution. Do a few water changes and enjoy!