Your Ec is fine , I mean not too high and your cal mag is giving extra nitrogen so the issue you could have is a Nitrogen abundance but your leaves does not seems dark green so I guess it will be fine as your new cal mag will not provide that much N. Concerning your root rot I can't tell you exactly what did that but I can tell you that 17°C for a day temps is way too high and will stunt your grow , I guess that your water temps should be the same ( a bit low ) and your night temps must be lower 😓 you should find a way to reach higher temps during day time and night time and check your water temps to know if you need an aquarium tank water heater or something like that 😊✌️🏼