I have had 250W HQI over a 29 gallon with no issues. Heat can be an issue if you do not have a fan, but 150W HQI is not all that hot. This is a great light - best of breed and you cannot really do better. If you do need a fan, get a Vornado and don't jack around with a computer/DC fan.
People think that too much light is an issue, but this is mostly from the thumb suckers of the hobby. It most certainly is not if the quality is good. Sure, LEDs can burn corals, but it is because the spectrum is junk, not because of the quantity. Quality matters a whole lot. You cannot really give too much high quality light to a coral. I give more light with Halides than people would kill their SPS under LEDs... 750+ PAR in some places and the stuff shines and thrives.
Keep in mind that these are under about 2300 PAR and have to overcome some harsh conditions, yet are thriving... makes you wonder why a Radion at 50% will kill coral at 300-350 PAR (or maybe it doesn't if you are thinking clearly):