This is my method for speed growing green algae on rocks in a dedicated tank:
I use a small shallow glass tank positioned near a window in direct sunlight, with 2 x 15w bulbs and reflectors fitted in the hood (obviously the stronger the light the better). The flourescant tubes are of the optimum frequancy range for chlorophyll photosynthasis, and are left on 24hrs a day. Rocks and paddle stones of various sizes are placed in the bottom, and i use old tank water left over as a result of my weekly 15% water change in my river tank. To the water i add Nutrafin 'plant-gro' at the rate of 1ml per 1 litre of water. Any plant food could be used, but i have found this to be the best as it contains nitrogen as well as iron, manganese and zinc. Also added to the water is Waterlife 'Bio-mature' which is another source of nitrogen in the form of ammonium(algae's prefurred source), but only 2 or 3 drops per 10 litres of water, and finally waterlife 'vitazin' a multi vitamin suppliment(vitamins encourage algae growth, B12 especially), at about 7 or 8 drops per 10 litres. 50% of the water is changed for new (enriched with nutriants as above) twice a week to keep nutriant levels topped up. I also use a small airstone in the tank, which boosts growth even more, presumably by increasing levels of dissolved CO2 in the water.
I have great results using this method, and it produces enough lush green algae to feed my 9 hillstream loaches with it every other day, which they really appreciate!

I hope somebody finds this useful, and if anyone has any ideas to improve this method even further, or any other ideas for speed-growing algae, please let me know.
Gary