This thread is getting rather old, but I have to agree to disagree. To a newcomer to the planted tank hobby (like I was a year ago) NO JOKE I had a third of a watt per gallon of "marine glo" light over a 60 gallon tall, and I thought I could grow java fern and java moss, because they are often said to be low light. "But it looks bright" ... I actually thought it looked bright until I added 2 more 39 watt bulbs.
Admittedly, it was probably the spectrum of light and the inhabitants of the tank (tinfoils) that hindered the most, but a newbie thinks that a low light plant means less than one watt per gallon, because that is what their tank came with. They also don't want to get pressurized CO2 or dose any fert at all (though like ROBERT H said, they would rather dose a fert than change the light) and expect results!
I have had plants sit there doing nothing for a couple weeks in such light levels, they are indeed not healthy and disintegrate after the fact. I had cabomba in 0.67 watts oer gallon and it sat doing nothing for a month, then it sent up a side shoot, (it "grew!") then it lost all it's leaves. I think really it is the water parameters and the nutrients that matter for most plants. I grew milfoil quite well at 1.4 watts to the gallon, with no CO2 or dosing ferts, though it was native (so the PH and hardness were similar...) and there was little competition for nutrients. Eventually it crashed, the tips shrunk, turned highlighter-yellow and disintegrated, but that was likely from too few minerals in the water. AT the time, I thought 1.4 wpg was medium light.
ANYWAY, I dunno what to think right now... Adding tons of CO2 seems to make sense, probably at low light some plants are better at getting enough CO2 than others, so pumping it in helps them get some... But I don't think 1-2 is low enough to be called low light. Even so, I have a few plants I would add to yonder list:
Chara sp. (macro-alga)
BOTH were grown to decent amounts in 1.4 wpg with no ferts. No CO2 either.
SO my diagnosis is: If you have 0.6 wpg, want a microsword carpet and don't want to upgrade, TOUGH. Upgrade it, get CO2, and do the EI method. Otherwise, stick with java fern and java moss.
PS: I have never EVER owned any crypt or anubias or hygro, so don't hate on my 2 cents.
My tank sucks now
Fraternity of Dirt # 22