I am not familiar with the nutes you are using but my guess would be they are not PH stable if they are fluctuating that much. Is it a one, two or three part nute? If more then one part add the micro nutes first then the macro, test the ppm then check the PH. I would not add any PH up at all for any reason. If it the PH gets too low just add more water. Make sure you are mixing everything separate from the reservoir and only adding it when it is close to the same PH to prevent the shock and the leaf curling.
The white on the rooter cubes probably not harmful but if it bothers you, mix up some hydrogen peroxide and water in a spray bottle and give them a spray. Should clear it right up.
Just between us, I don't even own a ppm meter
