dude, if the roots are browning its the start of pythium aka root rot...check your temps cus some nutes will make your roots brown i got nasty root rot and hygrozyme fixed me right up, get one of those 3$ aquarium thrmometers and check temps or you can lose the whole crop, and yes root rot will stop the plants growth dead in its tracks...look for temps under 75F....for the meantime you can add hydrogen peroxide, depending on what strength you have if its regular 3% 2 table spoons a gallon would do every 3-4days...is there any way you can get a pic of your roots?