Identification: Brugmansia leaves are light green, witty and some are falling off

I have a brugmansia that I repoted in Summer 2015. I left it out during the Summer and it did amazing and even grew a second be achieved! I am so excited as it is getting one step closer to it blooming, finally.
However, recently in the winter months I have noticed it not doing so well. The leaves on the plant started to become light green with some curling on the leaves. The leaves have been randomly falling off, about a dozen all together since it came back in doors.
I water it on a weekly basis but recently held off on watering to see if it helps. Nothing has changed. Also, I have drilled a hole at the bottom for drainage.

I noticed there has been fungus gnats in the soil and put some sticky fly trap around the plant.

Attached is a couple photos of the plant.

Let me know what your suggestions and advice is.

Thank you!

 

This is what it looked like in the summer (2015)

 

Hi Jordan. Forced air heating in a northern climate makes for very dry air. Brugs usually can't survive a winter indoors like that, without perhaps raising the humidity & light (a lot). A pebble tray is likely not enough for humidity.
I winter mine in the garage under lights, but first I strip off all but the smallest, half-developed leaves. The plant can't support all those leaves in dry and (relatively) dark of our indoor houses. I also like to shake off the top 1/2" of soil and refresh it with a soilless mix to limit fungus gnats. If you really want to knock them out, get the liquid drops with live bacillus thuringiensis israelensis. Pond supply stores always have them. A few drops in a spray bottle of non-chlorine water will do the trick within a week or two.
If your garage is very cool, but not freezing, it's perfect. It slows everything down, raises the humidity to safe levels, slows & limits the leggy undesirable growth you get indoors, and really reduces your exposure to bugs.
The more warmth you have, the more light & humidity you need, probably more than most of us can ever provide; so get it cool ( and light if you can but not required), and strip off most of those leaves, because they'll fall off soon anyway and just attract sucking insects.
Consider planting it in the ground next year. With enough fertilizer you could have a six foot bush loaded with giant, fragrant blooms by the end of summer. :)

 

Thank you Tom! I think you hit the nail right on the head. Now that we are in March, would you still recommend moving the brugmansia to a cool spot? The only place I can put it is in my basement which has very little natural light.

 

The basement sounds fine if you are still subject to frost or freeze. I'd imagine anywhere in Ontario would be. This is a tropical plant. There's a large brug near me. Noticed today that it is full of blossoms, but it's a little leggy and leaves are small and scarce since it's outside in the ground. It would have dropped most of its leaves in our subtropical winter. Doubt we had any freezes this year and it's warm enough that I might transplant tomato seedlings soon. Do not leave it indoors in the dark past your last freeze date. It needs a lot of sun and warmth. Probably a west facing exposure if you have it. Or maybe that far north, it needs southern. Been years since I lived up that way.