Are you sure it's a problem due to pH lockout? How old are your seedlings? Have you begun to fertilize them? If you're pH is not so far in either direction to cause harm to the plant, it's probably not lockout. If the seedling is still feeding from the cotyledons, then the pH is not as important. pH is primarily important for the plants to properly take in nutrients. If they don't need the nutes, it won't matter.