Its quite hard to say really looks like there may be a couple issues
The yellow and upcurled tips look possibly like a combo of nute burn and heat stress , the lower bit were its brown and started to be eaten away looks like a ph issue , can someone confirm if water needs ph'ing if using soil? From what ive read the soil buffers it
I guess the 5litres was to flush it would need more than that , the lower droopy leaves look like over watered and the newer leaves look underwatered as the stems dont look like they have weight to them , id back the light off it maybe 4 inch , if you have a fan in there turn it upto full wack for a couple of days get some oxygen to the roots just dont put the fan directly on them just below the light and above the plant should be fine
Early overwater/underwater issues can cause root problems , id let her dry out completley then give her the big flush , put it in the bath and run water through it for 3 minutes , and then put 6 litres of plain water thats been left out for 24 hours through it with no other liquid
, shes still saveable one of mine bounced back from looking alot worse than this , took roughly 5 days after a big flush...
By the way guys i am a newbie grower myself so any input from an experienced grower might be abit better , thought id add my 2 pence worth

s