cf / ppm problem

HI all. I am in weeks 4 flower in bubble hydro useing flora and have been very very care full on inputting nutes. But i check the res ppm yesterday and its at 2.8 (shit) it should be 1.6 tops at the moment and nothing as been added. i drained and refilled with water and it was .8 the the next morning without nutes it was back to 2.4 ????????????

why
why

i dont want nute lock at this stage.
 
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