Water temps and PPM questions in DWC grow

[420AsianNigro]

Im starting my first grow in both Coco and DWC
Due to my research water temp should be kept around 20C, 60-65F
I live in an area now temp around 5-15C, 41-59F
So the water will get really cold during the dark I suppose?
it's that gonna be a problem?

Another question
According to my FoxFarm hydro nutrient feeding schedule
The recommend ppm for seeding is 490-630.
but i also learn that not to use any nutrient during seeding from research
Should I use any?
Also any tips for first DWC grow?

Sorry for the poor english, not a native speaker

 

[rillos]

Don't let your nighttime temps drop below 61 or you will have several issues

 

[420AsianNigro]

Don't let your nighttime temps drop below 61 or you will have several issues

Can you explain more?
I use to live in CA, where temperature during the winter is also 41-60F
I've never seem a grower using a heater
instead they need a water chiller
I'm confused

 

[Old Salt]

I'm growing in coco, and have a space heater in my grow tent. It was originally set to 65°F.

If you have large temperature drop in your grow area, and insufficient ventilation, you'll run into humidity problems. The water carrying capacity of air doubles with each 10°C or 18°F rise in temperature. This means that if your nighttime temperature drops to 60°F from a daytime high of 78°F and an RH of 50%, the nighttime RH could easily rise to 100%. Good ventilation, and a little heat, say 5°F, will help with this as well.

Other options to control temperature include placing insulation under the tent, and between it and the outside wall. I had condensation on the inside of my grow tent, and corrected it by adding the insulation, increasing the minimum temperature to 70°F, and increasing the airflow. The nighttime temp now never drops below 70°F and the RH never increases above 64%. That's still a little high in flower, but much better than the 85% RH I was reaching on the coldest nights.

You can see the heater in the lower right of this image:

Day 67 of the Grow / Day 42 of Veg​

The tent is 2' X 4' X 5'.