Probably the easiest way to test for metals is to take your water to the pool store to have it tested. Most of them will do it for free. Be prepared to resist the long list of "stuff" they're going to tell you that you need, though, unless you DO have metals, in which case you need to get a sequestrant (Metal Magic, Jack's Magic, etc). Usually if metals is the problem, it just creates a stain, though, not bumps. What is the source of your fill water? If it's not well water, then chances are pretty good that' you're metal-free, unless you've added it in the form of algaecides or other chems.

Janet