Yo Geno - thanks for confirming and wow i thought maybe 50L was just a typo, but fair play if they are as no harm in going big!
Firstly then, if they're in any sort of general, average soil, I'd be surprised if the plant has finished off all the nutes already present, so potentially your soil hasn't needed a feed top-up yet anyway, and therefore yes, adding more nutes can potentially cause soil to get hot and cause nute lockout. Yet, again, in a 50L pot, you'd have to be really pumping feed nutes in tip ph balance of a pot that size, so i suspect overfeeding itself isn't the problem at this stage, and like DPhipps says above, it's just the over-watering on it's own which is causing problems.
Another potential factor is, depending how you potted up & what rootball is like determines food & water uptake - if they got good, solid rootball then it'll be feeding from most of the 50L pot which is good and so yes, potentially could've used up food already. But if rootball wasn't big before going in 50L then you could have ended up with tap roots going straight to bottom and essentially all food above them is ignored - watering will trickle nutes down to them eventually, but development of good rootballs is the key to using any size pot and getting plant to eat & drink effectively.
I would agree too about leaving to dry out for few days and once pots feel lighter should help and atm flushing with anything will probably compound your problem. Certainly if a flush is needed, some people would just flush through now on the basis wet is wet, but me personally I'd prefer to let dry for few days, get the soil abit more aerated and then flush properly, accepting the sacrifice of a weeks growth delay. Have a search on here for more expert flushing tips first if you are intending to do it, though i honestly think over-watering is the only issue here.
And once you resume normally, space out watering days abit more as a 50L pot should retain enough that every other day is not needed - i would guess even once a week is fine with pot that size. Feed wise, it's totally dependent on what the plant looks like it needs, so I can't offer any advice beyond go lightly if not sure. Only other tip to give is weed doesn't like constantly moist soil like you would expect with other plants; weed prefers going through wet and dry periods so don't be scared it's gonna wilt and die the second you don't water it - they can tolerate dry periods ok and it actually helps with root development (though week 4 flowering is bit late to be worried about root development, so just bear in mind for next time!)
Feel free to post any pics if you can, as i am only guessing from afar! Good luck anyway bro and hopefully once they dry out you'll see them soon bounce back!