vince

Using water from a fish tank is okay, Providing? your fish were surviving, remember your plants in the tank are using up the nitrogen under lights.
Your biggest prob. in a tank is Nitrates, but your filter should take care of that.
As far as a Fukien? they are one of my " Nemesis "
Can be very touchy. I read somewhere to cut off all flowers as soon as they sprout, this i have done, and so far so good, this is supposed to encourage leaf growth, have had it for over a year, this is a record for me.
Have it under strong lights with some Ficus, this keeps the leaves small, but i don't think i would worry about large leaves at the moment, keeping the damn thing alive is the main thing. Cheers.