Might be light...its way down by the base on the branches too though. Think thats burnin the tips too? Im runnin 3 100w rapidled pucks at about 75-80% in a 3x3 tent on one plant. But theyre up at least 2ft off the plant. I used to have em spread out more with 2 or 3 plants though.When I see that it usually means its hungry. You can either increase nutes a tad or back off light a bit.