I use 5ml for each new 2L bottle of phyto. For example, when I have used 1 of my 2L bottles down to 1/3, I add 5ml of Miracle Grow and then fill the rest of the bottle with saltwater (my phyto specific gravity is at 1.019). When splitting, it is the same, I will take 1 2L bottle of cultured phyto and split it into three 2L bottles...add 5ml of MG to both and fill with saltwater. It typically takes 4 days for a bottle to get nice and green and I use a three foot shop light with 2 fluourescent bulbs from Home Depot. I typically am culturing 4-5 bottles at a time though, I easily could have used a two foot one. You can try the strip light, it may just take longer to culture without having a broad distribution of light over the bottle.