Nickel is a an ultra trace element that we need, but it is also toxic in higher doses. Please consult your doctor if you are considering nickel supplementation.
Manganese is one mineral you are unlikely to have to supplement in your diet. It is involved in many enzyme reactions as it is a co-factor required by the enzyme. It is involved in removing free radicals as well as regulation of sugar release from muscle and liver tissue.
Strontium may not be required for good health, but it can help build healthy bones since it is chemically similar to calcium.