I disagree about the very expensive part. You can get 2 liter bottles of excel for about 19.99 at petmoutain.com (
Seachem Flourish Excel Plant Food) I double the dosage daily on my 75 G and it lasts me over three months.
So even if you buy it exactly every three months you are spending maybe 100 a year. I just bought a compressed co2 tank, regulator, hosing, and stuff to make a reactor and it cost me about $300.00 and I still have to buy CO2.
So you can use Excel for a long time before it catches up with the price of compressed and if you mist and burn through CO2 a little faster Excel may always be cheaper.
Excel is a great product but I went compressed so I was less restricted in my plant choice (My vals didnt like excel) and I was looking for slightly better growth. Up to date the tank in my signature has used excel for a carbon source. I recommend it to anyone especially someone just starting in the hobby as it seems to help with algae and the intiial investment is smaller.
I had 160 Watt of t-12's and next to non existent reflectors
dosing for my 75G was:
1/2 tsp of Seachem Equlibrium at water change
1/2 tsp of KNO3-2x a week
1/4 tsp of KH2PO4-2x a week
about 10 Ml of tropica plant nutrition-2x a week
You could probably go with
3/8 tsp of Seachem Equlibrium at water change
3/8 tsp of KNO3-2x a week
3/16 tsp of KH2PO4-2x a week
about 6-8 Ml of tropica plant nutrition-2x a week