[caseyhoo]

I keep most of my VFT at direct sunlight with water tray around 1.5cm.

For light for VFT... I think, you need to test and error. Difference of lighting tube, wattage, light color, what is distance between urs plant and light may give you difference answer for yours question --> how many watt i need...

My friend, he grow VFT in a 2ft standard aquarium using 1 philips 865 PLL 36w. It growing nice...

For yours VFT, it proabably is stress with the changed environment... So, just do what you can, mainly to increase lighting....