Dwc ph issues

i changed the solution yesterday and the ph was at 5.8 checked this morning and it was at 4.0 wtf help please ive also noticed a little blueing on some of the leaves but not all plants same system though. i think its a nute deff. is this right? temp stable at 76.0 rh at 40% dont understand why this is happening. Ive got some staw and blue going so i dont want to screw this up any advice would gratly be appreciated.they are only ten days old to soon for all this to be happening.

Falling pH is an indicator of Root Rot,
which you definately have.

You need to add some hydrogen peroxide, to kill the rr,
and then you need to keep the temp below 70º,
to prevent it's return.

.