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Low light experiment

Well, after being too lazy to move a MH 175 watt light I left a 54 watt
light on a 24 x 24 x 24 inch cube aquarium(60 gallon).
I will add the MH sometime but am interested in the results thus far with
the 54 watt light on a 60 gallon tank. At 24 inch depth and a thin/shallow
2-inch layer of onyx gravel no one would call this a high light tank by any
standard. The tank has lots(about 2.5 sq ft) of well growing Amano pearl
grass of the two leaf per node type, pennywort and some Crypt spiralis.
The tank is doing great and I have not cleaned the glass for over 3 weeks
now. I've been adding the normal KNO3, TMG and PO4, but no K2SO4 this
time(forgot to bring it down the tank's location). I doubt not adding it is
having that big of an effect. Perhaps later when there's more lighting it
will. There's little source of NO3 except for the KNO3.
P has been .6ppm and the NO3 4ppm after dosing and additions have been added
about every 4th day. TMG every 4th day 8-10mls. I'll be testing the usage
coming up here next week. Didn't test what they were prior but they must
have close since the readings after the additions were so close. CO2 has
been high, about 25ppm during this time.

I've often said and many others have as well that one needs the high
lighting to remove much of the nutrients. Low lighting is not enough etc.
My lighting is PC's but they are at less than 1 watt per gallon. I had a 55
gallon tank with 2 x 40 watts or about 1.6-1.7 watts a gallon and had the
same experience. I dosed it at slightly less than the other high light
tanks. Color type of all tanks are similar(5200K and 6700K mixes). I would
certainly get bushy denser growth if I had more light.

But my point is that algae doesn't appear at low light levels even if you
keep the nutrient levels the same as the high light tanks. The lower light
tanks use less of the nutrient per unit time(isuspect but as of yet need to
test for) but the algae also grow slower so they are held back in the same
manner as are the plants in this case.

This leads me to think that lighting is pretty flexible if nutrients/CO2 are
kept in a good range. So even a low light tank can handle higher PO4(.5 to
1.0ppm, there's little need for more) and lower NO3 levels(5-10ppm) like
many of our high light tanks. Dosing will likely be less frequent etc but I
wonder how much less. I've settled on  a one day longer(4 vs 3) days
approach between dosings.

Another issue is plant type in this tank. The other 55 had many species.
This has only 3. Quite a nice tank for less than one watt a gallon at 24inch
depth. I'd certainly think no way but sometimes things can surprise you. I'm
scratching my head some still. Also, there's not a herbivore in the tank
except for perhaps 6 -10 ramshorn snails.

Regards, 
Tom Barr