main cola not flowering

Hello community,

im growing an auto big bang, and has been flowering a few weeks. The main stem has had only 1 set of pistils on each level at each node (essentially 2 pistils per level), however they are beginning to turn red without growing the bud or further pistils sprouting. The other side stems shooting off and the top of the main stem have many pistils/ and decent bud growth, and these do not look a concern. I thought perhaps its because the depth of the light into the plant could be improved, however random bud is growing healthily near one of the base level of the main stem suggesting it is getting sufficient light? Does anybody know whats going on?


any help would be great

info/pics...........