Early stages of burnt tips

A question from a fellow grower:

Lately i see a broblem in my girls leaves that was mynor and started as early stages of burnt tips.
Im using bionova “dedicated” chart with Rain water. Ph around 6.0 in the solution gets me to 6.3-6.5 in the water that comes out the botom.
Im in the begining of 4th week flowering and last two I water I used half dose of the “soilsupermix”.
Would apritiate any help

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