Hello luvrin, your girl is looking good.
The red is due to stress she is having, probably the cold envirement.
Its not gonna kill her, its only gonna make her stronger if you act on the signs.
So not to worry.
To answer your question, your tempreture day and nighttime is way to low at this stage.
Your still in veg so it should be between 28 and 26 degrees celcius and at night between 21 and 20 degrees celcius.
In flower its different you want it to be cooler as you try to copy nature itself.
week 1, 2 and 3 of flower 25.5 at daytime and 18 or 19 at night
week 4, 5 and 6 of flower 24 at daytime and 17 or 18 at night
week 7, 8 and 9 or more 22.5 at daytime and NOT lower than 15.5 at night
Put a heater inside your room of growroom.
As far for your ph, i would crank it up to 6.5 at this stage of veg.
I hope this was an helpfull answer.
Keep on growing my friend. Peace 👍