I'll just answer a few of your questions sir.
75 gallons RA?!?! its not esy to maintain that big a tank. MIne is even only 60 gallons and the maintenance is already kinda difficult.
What are your tank dimensions?
18 watts for a 75 gallon, that would be 0.24 watts/gallon (wpg)
Here are the lighting measurements:
1.5-2 WPG low light
2.5 – 3 WPG medium lighting
3 WPG ++ high lighting
Here's more info:
Welcome to Aquatic Cebu Enthusiasts! - Re: Introduction to Lighting - ACE
i usually go with medium lighting since its can grow almost any plant.
Good luck with your set-up.
0.24 watts/gallon
pls pm me your DIY recipe.