In my soil grows I always shot for a PH of 6.3, but anything between the 6.1 and 7 range from my knowledge is acceptable.

I never suggested the soil maybe radioactive, and I was more or less throwing it out there as a funny, there are only a few areas that have any sort of radioactive water. Such as certain areas in idaho. So its highly unlikely this is the case.

I'm leaning more towards a hot soil batch than anything. Remember though, if your flushing your soil to balance the PH, your also flushing the nutes in your soil. Which is of course better than nute burn. Also, your idea to cover the clear container for the roots is a good idea, roots don't take well to light.