My plants welting and diying one after one

[baxbax]

Hello
I have this grow journal : 3 x Cotton Candy - 400W HPS - Indoor - Coco Coir/Perlite

my one fem good plant died : My old seedling damping off - help

other one died too cotton candy

and this one is dying too :

just one plant cotton candy look good but no grow no grooooooowwww

Hey friends I'm growing over two month I don't know what I'm doing wrong ??

How many plants? What strains?
4 plants 3 cotton candy (2died ) one spoetnik 1 welting
How old are they?
over two month about
Indoor or outdoor?
indoor
How big is your area if its indoors and is it well ventilated?
I have 1 blowing fan and don't use exhust fan it's off now because they are little and i'm trying to save rh 110 * 75 cm
What medium/soil are you using?
coco peat mixed with perlite
Whats the size of the containers?
about 0.5 litre
What's your lighting set up? 400 w mh
What's the temperature and humidity like at any given time?
temp is 21 25 and rh is 40 about
What's your ph like, both medium and nutes?
my coco run off always is 8 and my watered and nutes mix is always 5.8 6.3 about
Any pests around?
no
What is your watering schedule like?
every 2 or 3 day with nutrients npk 20 10 8 and sulfur and cal-mag

what I'm doing wrong ??

 

[jzombie82]

Somthing is up with your ph that should melt your buckets if its that high. Are you watering with just phed water between feedings? Maybe?

 

[baxbax]

my god ! root rot I checked they are brown and soft not white and crispy yes my plants roots rotted I don't know why my runoff ph is that high because of that I was flushing several times every day and maybe this cause my root rot other died plants too ... how I can treat this rotted plant imediately to save them ???

 

[Stealthboat]

In the mean time here is an article on root rot: How do I identify and prevent Root Rot?
It might have happened because they were overwatered a lot. Adding in at least 33% of perlite to your medium should fix drainage issues and allow it to dry out faster. Not sure how else it could have happened.