How Can I Increase the Brix levels? Any tried and...

Unsulphered Molasses is good for feeding beneficial microorganisms in soil, probably a lot of 'bro science' out there but it's well worth spendin 30 minutes looking at the benefits of molasses in your grow, assuming you haven't already. Good luck pal

For higher Brix levels, go back to basics. Make sure they're getting enough light (you have 3 beastly lights, you need a PAR meter to make sure they're getting 600-800 ppfd). Make sure your nutrients are good. When EC is the same in the runoff as it is when you mix it, then you're feeding just right. Any slow release fertilizers in the soil change that fact though. Your temps look good. Some plants respond better to a slightly lower humidity. Defoliating can increase Brix. You're looking for about 15%. Make sure you've dialed in your refractometer correctly. Wish I had more for you, I've never gone out of my way to measure my own levels.