my 36watt compact florecent light used to be on my 15gal tank giving it 2.4watt/gal which is ideal for plants. they doubled in size within a a month or 2 of use. now i got a 30gal tank and im still using the same light for it. giving just a little bit over 1watt/gal right now. my plants are doing fine..they are still growing. but im not sure if it enough for them or should i go with another 36 watt bulb bumping it to 2.4watt/gal again?

any ideas?

Don't rely only on wattage per galon to tell you if the lighting is appropriate. Do you have a 30g or a 29g tank? The 15g tank has the same height and depth as the 29g (18in), the 30g is shorter (16in). Thus, it would not make a difference if the plants are directly under the strip light. In addition, some plants will tolerate a wide range of lighting conditions. What plants do you have?

i have a oceanic 30 gal tank and i just measured it and its roughly 19-20 inch tall...my 15gal tank is 12in tall.

as for plants..i dont remember what they are, but they are in the picture in my signiture.

From the looks of the siggy, you have some Amazon Swords (Echinodorus amazonicus), Cryptocoryn and some Cabomba Aquatic. The Echinodorus and the Cabomba require atleast 2wpg, but highly recommend atlease 3wpg to keep the Cabomba happy. The Cryptocoryn can be grown is 1wpg and higher, so having high lighting wont affect it. I had Cabomba in a tank with 3.5wpg and it was flourishing and in a 2wpg tank, it was losing its leaves like crazy! So i personally recommend some more lighting. Usually people with large tanks use Metal Halides. 150watts on a 50gal tank. That makes 3wpg.

Goodluck!
Mango