Issues with leaves. Day 90 total, 30 of flower. Leaves have been getting more and more yellow the past week, with progressively more brown tips.

The tips burning is caused by nutrient burn and the yellowing is caused by nutrient lockout. From now on you need to use nutritions that are rich on phosphorus (P) and potassium (K). You can use a PK Booster like Organoman adviced. Make sure that your pH is in the right range otherwise the plant will be unable to absorb the nutrients. The right pH for soil is 6.5

The leaf tips curling and browning are signs of over feeding to me, and depending on whats in the medium it can lock out other nutrients thus mimicking a deficiency but in reality its a lockout. If your just using coat of marine soil it might need a bit for fortification if its not a lockout, I know its an all in one feed but i forget if its NPK ratios are used up in the same manner. also there is the transition from Veg to Flower that's making it use more P and K from the medium. One thing I would try is lowering the PH down to 6.5-6.8 and see if that helps at all. The next thing I would do is look into giving it some magnesium, then monitoring the EC of the soil using a slurry test. if the mediums mixture is not that high in EC it need more food and the tips burning could be from the light being to close and hot temps. I always find my cannabis needs extra Magnesium though. Best Of Luck!