Gorrilla Glue (first grow)

I forgot to take photos the previous week, but the plant seemed to grow great, lots of new leaves and growth, watered once. It takes about a 6 - 7 days before the pot is dry which seems a bit long but I hope this will improve once the plant grows. But the this week I spotted a brow spot on one of the first leaves. I started to read up on what it could be, and thought the most possible to be ph fluctuation, nutrient burn or overwatering. I flushed the plant a day after spotting the first brow spot with water that had 6.1 ph (or so I thought ...). The next day, the brown spots were much worse, even starting to appear on higher level leaves. I read up some more, and found out that shaking the water temporarily raises its ph levels ... Well before taking the final measurement, after adding some ph down i always shook the bottle to mix it ... This made the ph fluctionation problem the most probable one in my mind, So the next day I flushed with this time hopefully good water with ph of 6.6.