Add the HPS when you put them into 12/12 for flower.
They will like the mixed spectrum, and doubling the wattage for flower is perfect.
Just make sure your electrical circuits can handle it, and that you have enough ventilation or AC to control the heat.
psteve Reviewed by psteve on . mh to hps when to change?? i have my babies under 1000w mh and have been for 3 1.2 weeks now. when is a good time to change to 1000w hps? or is it ok to do a combo and when is a good time to start either way? 3 are about 14 inches tall with good leaf sets on them.and the other 10 are around 9 inches tall.heres sum pics to see. Rating: 5