What I have picked up from the boards is that PFO MH is the best for the Iwasaki 6,500k and good for the others like the 10,000k. The HQI is the best for the 20,000k and the 10,000k, and essential for the double ended HQI bulbs they were designed for. There are photos on this website's library, and a long running thread on reefcentral with about 10,000 viewings
