First, the wpg rule is basically useless. What kind of lighting do you have? What size of tank? The carbon that can be dosed is most likely Seachem's Excel. What this does is provide a liquid source of carbon, it is inferior to actually using a DIY CO2 setup, and certainly no where near a pressurized system.
Tanks less than 30 gallons can usually use a DIY co2 system fairly well and tanks larger than that will greatly benefit from a pressurized system. Obviously there are huge costs difference as DIY costs about 5 bucks to get up and going and pressurized can cost anywhere from 150-400 depending on everything you buy. Just using Excel can get expensive as well if your tank is large. I would recommend just saving that money and getting some form of gas CO2 going.
Research these two methods and decide what is right for you. Then the forum can likely assist you in deciding what kind of equipment you need.
Tell us some more. I assume you are moderately planted. (a picture would be nice!) What size tank do you have. What kind of light fixture do you have now, and what kind are you going to change it to. How many fish. etc.
Carpeting plants do best if you have good CO2, which means pressurized CO2. Excel is better than nothing, but not nearly as effective as CO2. If you really want to go that way, first save up and get a pressurized CO2 system.
I got this marineland led fixture that has 1670 lumens and im ready to return it if its not as good as 4 t5 bulbs over my 37 gallon tank.I was gonna get a t5 ho fixture that has 4 24 watt lamps but the LFS told me that this led fixture was pretty good.My tank is pretty tall like 22" so thats the reason why i want to get a quality fixture.
That Marineland double bright LED light isn't even close to giving as much light as a 4 bulb T5HO light. But, you also don't need even close to 4 T5HO bulbs over that tank, so it might work, but only for low light.
A 22 inch high tank is about the lowest tank that T5HO lights are appropriate for, other than single bulb lights. And, a two bulb T5HO light should really be raised about a foot above the top of the tank, assuming the light has typically very good reflectors, and that you want to have only as much light as you need.