Mike, to answer your questions I will try my best. As for cost I am assuming you mean what you need and savings you will get and being green. Is it a bow 155 6' tank? You can get away running 3 modules to start as long as you can hang them high. You can also add more as needed in the future. There is no bulb replacing I changed my bulbs every 6 to 8 months so I can see that savings in my part and less work. My lights all on run about 1.8 amps electric savings. Let's see the look and the possibilities are endless. Cloudy day, thunderstorms, 29 day lunar cycle should I go on. Ok here goes I have the lights if you want to check them out before you buy them PM me and i'll be happy to show you if you have any other questions about how powerful they are let's say had to turn them down starting to cook some corals. My highest settings are whites 30% blues 50% royal blues 55% and might need to turn them down again.