Looking like they're stretching well mate , never grown that strain bit as @zannabis7 pointed out , could maybe do with more light , I don't mean time in light , I mean intensity , I'd move my light closer to the plant as it seem to be using its energy stretching towards the light rather than fill out ... don't panic tho , looks healthy ! .. I noticed your using a 600w is it dimmable ? If so , I'd dim to 250 or 400 and move light closer to plants .. I'm no expert tho mate , that's just tips I've brought from photos
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