Nutes and water cycle question.

This is my first grow and I've been using RUI for pretty much all of my information. I have 6 females grown for a week in 12/12. Right now I'm feeding them with a low dose of Bud XL but will probably run out within the next week or so. I'm kinda on a budget grow so I was wondering what is a good nutrient to use??? I heard Fox Farm is a good brand or Advanced Nutrient. Also how often should I flush the plants???

I'm growing in soil too.

Some say once a week... others say once a month.
My grow this time, I'm going to do it every 2 weeks.
My last grow I didn't do it once, I had a average yield;
I could have done far better I'm thinking, .326 grams
per watt. 430w HPS yielded 140 grams of dried buds.
Foxfarm is always a good choice.