Sunflowers Indoors

Hi All, i am currently growing sunflowers in a grow tent which i constructed myself using reflective two tone (White Inside, Black Outside) PVC Sheeting. They are currently 71/2" tall and are in pots which measure 7" X 8". My Soil mixture is 75% Potting Mix (Organic/Fertiliser Free), 15% Perlite and 10% Building Sand. I Water them twice a day with a rapid growth hydroponic two part soloution. Just wondering who else out there has tried to grow sunflowers indoors before and perhaps heir results/past experiences with what to do and what not to do. This is my first time growing any plants whatsoever so any help is much appreciated. I have attached some Pictures of the plants in their current state of vegetative growth.

I Was using a 400w MH setup until a few days ago when the bulb blew and so i just used my 600w HPS instead, although i have noticed no difference in the growth rate between the two bulbs, apart from the redish glow that now comes from the tent. Temperature seemed easier to control with the MH however, as it stands using the HPS my daily temp is around 28C with a relative Humidity of 60%