Leafs dropping

Its either under or over watering. In flowering the plants will start to use less water. Go off sticking your finger in top of substrate and picking up the whole planter. Water weight is heavy. If it is staying super wet and heavy even before watering then it is too much. But if it is light and dry then not enough. In your case I think half a gallon a day is too much. Problem is too much water, the plant is drowning. It needs time to get air in roots and breath. Go to ever other or every 3 days depending on weight and feel test. Happy growing and good luck

It is water damage! but not under-watering rather too frequent irrigations. Try letting the top 5cm of the grow medium dry well before irrigating again, but dont let the medium dry completely! Also remember to irrigate until there's at least 20-30% runoff! Hope this helps! Good luck and happy growing :)