Problem Canna

I've had this white canna (don't know the name) for almost a year and a half. About 2 months ago it bloomed like crazy, now it's stopped blooming and the leaves are getting brown, crinkly and crunchy.
It sits in a Southern-ish facing window and gets plenty of bright and direct light.


Now, I Think it's because of the Bayer rose and shrub stuff I used. It acted as a bug killer and fertilizer, and my main thing was to kill spider mites (because it was becoming a right infestation) ((at the time I did not know water, water +soap etc. could kill the mites)) and I used the Bayer product about a month ago and now my leaves are turning funny. I have since returned the Bayer stuff (because it stank to high heaven and it certainly didnt take care of any spider mites) and now whenever I water this canna I soak it so that plenty of water drains out. The water is usually a very poopy color brown.

So, as long as this got, any opinions to the matter would be lovely. I'm hoping that after I douce the plant with plenty of treatments the 'toxins' will leach from the soil so the plant will recover. Whaddaya think?

This one also.

Huh, I dunno. But the curiosity is killing me.....why are you growing canna inside in Fl? Whatever is wrong with it could certainly be fixed by planting it outside. Have you taken a peak inside the pot to make sure you still have healthy white roots? When it comes to pots, my first thought is always that something has gone awry in the pot.

Well I could put it out on the patio, but I live in a condo so I dont have a yard. It was doing fine inside for the longest time.

Oh, I see. Still....have you checked out the roots?