Northern Lights Auto First Grow

There has been quite a large amount of growth this week, one of the plants grew to a whopping 19cm tall. I fed the plants twice this week at 1/4 strength that Professor's Nutrients recommends at a pH of 5.8 and watered once with regular water at a pH of 5.6. The redness that was present on some of the stems last week has all but disappeared, however there appears to be some discolouration on some of the leaves as the tips are slightly turning yellow. I will monitor the plants closely for the next few days to ensure that the yellowness does not spread throughout the plants.