Really low light for plants

Nov 5, 2016
I have a 39 gallon with24" 17watts T8 light....6500k, 85 CRI...Trying to grow Amazon swords, Java fern, Anubis's... keeping light on 9 hours a day with liquid ferts...twice a week...There doing OK staying green all but the Amazon Sword...turning yellow and pale...Almost a year now since I started. Don't really want to get better lightning unless I have to


Superstar Fish
Jan 11, 2013
East Aurora, NY
Not sure of the footprint and height of this size tank, but that is an extremely low amount of light in terms of the PAR/PUR it can put out. I don't care for the old watt per gallon for fluorescents rule, but it is kind of accurate for T12, T8 and T5 fluorescent. Minimum recommendation is typically 2 watts per gallon for low to medium light plants. On top of all that, you need to replace your fluorescent tubes every 6-12mo because their PAR/PUR output fades drastically, as does their color/temp and CRI. It may look fine to the human eye and still light up fine, but that means little.