Whats a good hight to start flowering?

Hey everybody, This is my first grow. I have a 5 gal hydroponics system and I have 2 plants in it doing very well at the moment. So right now there about a month and a week old. I have them under 2 4ft 40 watt fluorescent tubes, cool white. I'm feeding them the flora series nutes. I also have a home made carbon generator, which I found out how to make on youtube. HA HA! Also I have a 150 watt HPS which I will use to flower them. It's all in my closet which has reflective paper and a fan for air circulation. So my question is how tall should my plants be so I can start to flower them? And also how often should i flush them with plain water and for how long. If any one can help it would be greatly appreciated. Thanks evry1!

Ive also attached some img so you can see what i have going on.

no need to actually flush them until the last 3-4days before harvest. But you need to change the nutes every 7 to 10 days and check the ppm and pH at least once a day. as for how tall you think you should go into flowering depends on how much room you have the types of plants also. But generally you can count on the plants growing 2 to 3 times whatever height they are when you put them into flowering ie. 2ft at start will equal as much as 6ft at the end and maybe more depending on you feeding schedule, how close the lights are, and several other factors but in general 2 to 3 times the starting height.

So only flush like the last two weeks of flowering. And for flowering? They can be flowere at any time?

You don't say how tall the plants are. There are people here who go 12/12 from seed and others who grow monster trees. If you are going to flower these with a 150W I wouldn't let them get too tall because that lamp isn't going to give you a lot of penetration. If you are at one foot I would go ahead and change the nutes to flower, no need to flush, and go 12/12 on the lights. When to flush? Opinions vary here, some say as little as 3 days others 2 weeks. Some say plain water others us GH FloraKleen or something like that. I use plain water but, have not tried the others so they may have value. Best wishes and welcome to RIU!

Hey! Thanks for the info. I also just found pistils on one of my plants. So I know for sure it's pre flower and that it's a female. The plant is about 8in tall. So now I thinking of letting it veg until it reaches a foot. That way I can take clones from it. I'm so excited. This is my first grow and their doing good. Also I've been readind and I've found some information about cfl lighting. So right now I have 2 4ft cool white tubes, each tube is 40watts. So that's 80watts altogether. I know that those bulbs are on the blue light spectrum. But I've read that it's good to have a little red light spectrum in the veging stage. I'm not sure if it's true or not. I have a couple cfl lamps that are soft white. So they have red spectrum. Would it be good to add them to the exsisting lighting I have now. Or would it just stress the plants?

I use a mixed spectrum start to finish, you can and I would add them now.

Thanks bro! I added them today. So now I have a mixed spectrum. I'm gonna veg them for about three more weeks and see what happens. Now I want to take some clones from the one that is in pre flower. I'm gonna wait till she's about a foot tall.