Changing to Flowering Stage

I am using the Hydro setup with the tray, 400w Hps and Ive been in the Veg stage for 8 weeks. I think my plants are now ready for the flowering stage.

Whats the process to change to this?
I heard that I need to turn my light of for 24hrs before changing to 12/12?
Do I need to change my water completly as I have got 2 different types of food, one for the 2 stages?
What ppm shall i start with and increase to?

Please help as this is my 1st grow.
Thanks.

I grow in soil so I cannot help with your nutrient question. As far as the lights go you do not need to give them the total darkness for 24 hours. I have heard of people that do this, anywhere from 24 to 36 hours of darkness before triggering into 12/12 cycle, but I never have. I just put them in the flowering space and they are off to 12/12 cycle. This has always been successful for me. I hope this helps. As this is your first grow you may want to keep it simple.

Check my journal and the link I will post...

I am a soil grower- so your ppm questions I can answer--

But as for going from veg to flower- I will swear by a 36 hour darkness.... The period should range from 24-72 this is according to Jorge Cervantes and Arjan from Greenhouse- two legendary growers-

I am starting week 2 of flowering, and when I put them in i gave them 36- it worked coming out of the darkness 4 of them had preflowers- meaning they were girls... and after only one week- there were a total of 9 that had been sexed out of 11, leaving me with a total of 7 girls- I have gotten lucky with that male/female ratio!!! but either way- there was a ton of new growth after the darkness as well- and it has really helped me sex my plants out early...

Take a look at the journal...
and this link I started when I was deciding what to do when flower time came...
https://www.rollitup.org/indoor-growing/76790-36-hours-darkness-after-veg.html#post887625

Flower power
OB

btw WU TANG FOREVER! Fuckin rep wu to the fullest... Used to have 52 Wu and Wu affiliated records- serious WU head... but have dimmed quite a bit since a youngster- but still love their shit... Bangin 8 Diagrams in my car- George Clinton on that shit, and george harrisons son- how could you not!