I've been doing a little reading on lighting and was wondering if the type of bulb would matter for watts per gallon. I am currently running an aquatic life 36" t5ho fixture on a 75 gallon tank that holds 4 bulbs. The bulbs are all different that's why I have this question. 1x67000k coralife, 1x10000k coralife, 1x actinic blue, 1xblue coral I believe. All are 39 watt fixtures. Is it correct to say 4 x 39 = 156 total watts from fixture. So 156 / 75 = about 2.08 wpg. So I have about 2 wpg or my setup. I guess my question is do the colors of the bulb matter? Another question what kind of bulbs would be best for using for my setup as I don't like the yellow water tint from just 67000k bulbs? I do use co2.
Even though the watts per gallon rule is a bit outdated, it can be a step in the right direction to getting you to the right lighting. 6500K bulbs are recommended for planted tanks. These come closest to natural daylight at 5500K. The color is light blue to the eye.
If you keep to the less demanding plants, then 1.5 to 2 watts per gallon, even using the watts per gallon rule, puts your tank into the moderate light range. This amount will grow more than enough plants and a wide variety to fill a 75 G tank.
CO2 isn't necessary unless you get into the more demanding plants. When you increase the light, you tell your plant to grow faster. In order for the plant to do that, you need to increase the food accordingly.
A nicely planted tank isn't difficult. But, you need to research the plants you want and then give them the proper lighting, nutrients and pure water conditions.
Just a couple of thoughts to consider or not.