3 weeks into flowering pics

hi everyone, just looking for abit of advice on my indoor grow, currently growing ak47, im 3 weeks into flowering, ive noticed that the leafs are starting to turn pale green and yellow, also the leafs and stems are drooping over is this normal?
i fed them every 3 days with biobizz products they roughly take about a litre each which i think im under watering them.
should i only fed once, and if needing more just water for the rest of that week then fed the next week then just water the rest of that week?
i currently have them under a 400hps, temp stays between 68-78, and humidity stays between 48-55.
ive uploaded a few photos to try get as much advice as possible thanks for looking and hope to hear from you all!

happylarry
 

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