Leaves turning purple and purple stems

The clue is in the name "RED Poison". It has a genetic dominance for red/purple colurs! It is nothing to worry about and completely normal. Nice strain from my favourite breeder! Plant looks hungry though, give it half grow and half bloom nutrients for the next two feeds and she will finish much healthier. It looks as though you switched to bloom nutrients too early, cannabis still needs good amounts of nitrogen in early flower. What I have been doing for 25+ years, is to stick with grow nutrients for the first 2 weeks of flowering, or until there are small "budlets" formed, before changing to half grow and half bloom for the following 2-3 weeks, depending on flowering speed, before finally changing to straight bloom nutrients through until maturity. This seems to produce the biggest blooms, on plants that don't exhaust themselves and end up a sickly yellow colour by harvest time. If you go to te Sweet Seeds website, you will see pictures of this strain showing vivid purple leaves and stems too, so this is to be expected with this strain. Hope this helps, Organoman.