Hi,
Well, 150 watts over a 40G tank is a lot of light. Carpets don't require massive lighting to be lush although they can become lush faster with high lighting - but this is only if the high lighting is met with high nutrients, high flow and most importantly, high CO2. People make this mistake all the time thinking that lot's of light is required to grow plants. They don't realize that CO2 + nutrients + water grows plants and that light is the energy source by which CO2/nutrients/water are turned into food which is what fuels growth.
Imagine you had a house plant and were pumping massive lighting at it every day hydroponic style. Think about what would happen if you forgot to add water. The plant would soon shrivel to a look like a potato crisp right? Well, plants in water don't suffer lack of water but instead they suffer lack of CO2. People are forever forgetting that plants are made of Carbon, not light. Coal, the remains of giant forests, is Carbon. The Carbon that is the structure of plants can only come from the carbon in CO2. The result therefore of poor CO2 is that you have a carpet of lush mush. You'd have much better luck concentrating on optimizing CO2, flow, nutrients and distribution than you would throwing lots of light at a plant.
With the level of lighting that you have you'd better stock up on easy carbo and you'll have to dump massive amounts of TPN+ in that tank. Your CO2 gas consumption will also be huge and those filters will probably not be man enough for the task at hand. This is why I stated that it was a false economy to get the halide light so cheaply, because now you need to spend more money in order for the tank to survive those 150 watts of photonic bombardment.
Cheers,
