If you go with 250W HQI, they be equivalent to 400W single ended MH. I used 2 - 250W HQI bulbs running off a dual PFO ballast on my 90G, and it was more than enough light. I have a 180G on order, and plan on running 3 - 250W HQI bulbs off of PFO ballasts, and supplementing with VHO Actinics as...