Hi there,
Only speaking from experience...
1. More light would be my first suggestion. 90W is kind of low, especially to flower.
2. Looks like the plant needs more Nitrogen to me albeit for the burnt tips. I hit them with a bit of pk at this stage too but I wouldn't with yours because they are not 100% and could mess with it.
3. A bit of calmag may help too?
4. I only flip my plant to flower mode (if there is one) once I see flowers forming. Blue to grow, red to flower.