Plant not growing

Hi I'm a new grower and this is my second grow there both white widow big bud 1 isn't growing it's stopped and the leaves are going yellow the other has been growing well but noticed this morning the edges are the same the temp is 28high 20low ph level 6 but I've just fed them at 6.5 to see if that was the problem rh is between 40-55% any advice I would be grateful thanks https://uploads.tapatalk-cdn.com/201...d61e8f390c.jpghttps://uploads.tapatalk-cdn.com/201...127e7f1542.jpghttps://uploads.tapatalk-cdn.com/201...8b9cf0fdef.jpghttps://uploads.tapatalk-cdn.com/201...78a8eb4733.jpg

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