plant problems

hi people. im in desperate need of help with my plant.
ok to start the plant is ,pot of gold, growing in a greenhouse (uk) the plant has been doing great up untill now.feeding on hydro tops grow solution a & b
100 ml of each solution to 25 ltrs of water,2ml ph down in water.the plant is fed on a constant feed ,with about 2inch of feed in a square feed trough.
ok now the problem.
leafs are going light green & the stems are purple on lots of the leaf stems. any ideas wud be appreciated.
thanks
dizzy spells.

if pics are needed,i can take some