Is this Nutrient deficiency?

First off my light touch the top of the plant and burned it a bit ,but the bottom leaves that are turning yellow on the edges I'm not sure about.Havent started feeding them nutes yet probably been past due what do you guys think?Also when should I go ahead and start Flowering?

Magnesium deficiency causes yellowing of around the leaves and in-between the veins....also it can cause brown spots on the leaves and it causes purpling of the stems......do you have any of the symptoms???

Yup looks hungry. At that size Id be giving her half strength cal mag, 1/2 strength silica, 1/2 strength yucca, and 1/4 strength grow nutrients already.

What kind of soil mix and what are the N-P-K values you started with? Are you using tap water or RO? Just curious.

Happy frog mixed with perlite. Use distilles or RO water. I like organic feeds like grow 3-1-3 and bloom 4-3-6.

It's not magnesium..

Looks more like surface burn. ...human error. Did you touch the leaves after handling pH down? Possibly drip something on her? ..although, I'm not using a good phone ATM