Here we go again.The AQUA brand UV rates it's UV's diferently than other brands.So the 15 watt will work for your 150.Actually thier 8 watt is rated for up to 200 gallon tanks,but the 15 was reccomended to me by the company rep.It's good for 200-500 gallons.But however they rate them,They are the best.Just be sure to get the bulb upgrade(gold pins),the quartz sleeve,and the wiper.