First Barney's Growing Experience

Started my first attempt at LST and tied some of them down. However I feel growing them in a "spiral" might be more effective to keep them low. As of this week the bottom leaves on most of them started to look "bleached", turning towards yellow in colour. The top colas on all of them look as if they have burnt tips, Pineapple Express Auto and Peyote Cookies #2 are starting to get spotty leaves as if drying out. Moisture level has been good, so I fear my grow lamp seems too powerful / close to the plants. Considering switching from 24h light schedule to 18/6 or even less PH also feels a tad high on most of them (6.7 - 7), so looking for simple ways to make the soil more acidic