My plants have nodes all the way up and down the stalk, and the upper fan leaves are getting quite thick and large. Easily, all 6 plants are over 8 inches and there are multiple areas which are reproducing which look exactly like the main top(s). Already, my 3 gallon tank is using about half a gallon a day. When do I start doing the 12/12? TY

I assume that these are seedlings, and they will more than double in height after you switch to 12/12. Some strains will triple in height.

So it's up to you, how tall do you want them to be when finished? If you want them to be 24 inches or less, then change the lights now.

HTH

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Yep.

Deppending on strain and what sort of light you are using, I would start flowing soon.

Depends on your space, if you have room for a taller plant, that's more bud! So yeah... do it if you can.