Store bought Peroxide an oxidizer not a sanitizer
FYI Peroxide is great at removing smells, odors, and contaminants but in the concentrations available at retail stores it is not helpful as a sanitizer or disinfectant (for example pool water where I use an ozone generator to remove contaminants but a black light to sanitize). If your tank regularly has city water, peroxide treatment can remove smells and bad taste, but the city water's chlorine is the sanitizer. Peroxide needs to be in 30-50% concentrations to be effective as a sanitizer. Regular Joes can't buy concentrated peroxide, and it is tougher to handle.
Just keep using bleach.
If the contaminant is chemical (from fracking?) you need to know the contaminant before you can devise the best treatment. And if it is fracking related the local authorities need to be made aware (they likely already are). Fracking contaminants are often toxic. I don't use well water in active fracking areas.