Hey, could some of you help? :)

[LoveGrowingIt]

I cannot impress upon you enough that you are better off looking at your plant and seeing what your plant is telling you than you are playing with a light meter. It's simple. Look at your plant.

I just flipped a tent to 12/12 a few days ago and decided I'd measure the DLI using the Photone app. Their website has a chart that recommends a DLI of 25. I tried gradually raising the light. At a DLI above 18, the leaves started showing light stress. So, I backed off the light till the leaves looked happy again. So, yes. There's no substitute for reading the plant.

I have not given Cal mag, I read that floraflex should be sufficient but that may not be the case?

If the leaves are showing magnesium deficiency, then it isn't sufficient. Plants grown under LED lights need a lot of Mg. It looks like you're using soil in fabric pots. Perhaps you could add some Epsom Salt to the irrigation water. That tends to work rapidly.