PPM's are jumping up by themselves? I think that MIGHT mean your plant is drinking more water, and not absorbing as many of the nutes. I was led to believe the roots have the ability to somewhat regulate the amount of nutrients they uptake to a certain degree...So your plant is thirsty, and not so hungry...Try cutting back a little maybe and see if it stabilizes?
Also, did you recently switch to flowering nutes? If you've only been in 12/12 for a week, and you switched to flowering nutes cold turkey, the plant might still be looking for nitrogen for it's stretch period, and not digging the bloom nutes.
Need more information...lol