Autoflower not flowering

Grow granny my ph os 6.4 Id have written more detail in the question but i was limited on word count. So the 6.4 ph is measured from run off turns out my pen wasnt working well and now im using an api test for run off. Also from what I have learnt about autos there are some seeds/plants that revert back to photoperiod like a genetic throwback from what Ive been reading I can chuck on 12/12 instead of the 18/6 to get flowering started but my question is as Im using the light for 3 plants and 2 are flowering onay under 18hrs if I flip to the 12hr cycle can I flip it back to 18/6 once flowering starts. Thanks for your help though

Leave the light schedule alone. As long as she is growing with no stress keep going. If your having issues, that can delay flowering time as well. Would have to see plant and have a lot more information to give a solid answer.

Autoflowers do not respond to light change - their flowering schedule is built in to them and they will do it on THEIR schedule IF given good treatment. The one serious problem I see in the diary that contains this plant is your PH - 7.4 is WAY too alkaline for weed, my friend.... it's going to hurt every single plant in that grow if you don't get it down! A range of 6.0-6.5 (growing in soil) is good with the "sweet spot" of 6.2.... Your Sweet Tooth could simply be reacting to that alone! Not sure if she'll ever flower - is she in pre-flower? If not, I'd worry... but I wouldn't give up. I would flush her out with ph'd water and check the PH of the runoff you get with the next-to-last gallon.... if it's not between 6.0 and 6.5, keep flushing - add in 1/2 strength nutes to your last gallon and then let them dry out completely before giving them anything more... I would also tell you to do the same with the other plants in this grow as you're only going to face problems with them, too... If you don't have a PH pen, investing in one will be the most important thing you can do for ALL your plants - it's something I wish I had scrimped and saved and somehow afforded MUCH earlier! Check out either Apera (I love mine) or Blue Lab... Good luck - and as for Sweet Tooth, only time will tell if you've stunted her too badly or if she'll respond to the flush and start flowering...