Possible disease in my calathea ornata plant?

I recently got a small calathea ornata plant that was about fourteen inches tall. I transferred it into a nice pot that should have enough room and used cactus soil, as recommended by a web site, for extra since there wasn't enough. It was flourishing the first two weeks, growing new leaves and growing taller. Now some of its leaves are turning yellow, starting with those at the bottom, and now splotching some of the larger leaves. It usually starts at the tips. I broke off the smaller leaves that this happened to at first, but now I see that it may be a bigger problem. It gets what should be the right amount of low light from my bedroom window, but I think that perhaps the air conditioner, though I keep it on only in moderation and it shouldn't be cold enough, could be doing this. Has this happened to any of your calatheas, or have you had similar problems with plants? What can I do to make my plant flourish again? Thank you in advance.

Possible disease in my calathea ornata plant?
Calatheas need a consistent temperature, humid atmosphere, and a draft free position. These plants will die if they don’t have adequate drainage. Their soil needs to be kept just moist with soft water and shade must be available or else the leaves will be scorched. The signs of over watering and under watering are the same - yellowing leaves. Check your watering practices.





Avoid using cold water especially with houseplants. This can shock tender roots. Fill watering can with tepid water or allow cold water to sit for a while to come to room temperature before watering.





Here is a link to an article that discusses bacterial leaf spots of Calathea. You may find your symptoms here. Good luck. http://www.doacs.state.fl.us/pi/enpp/pat...
Reply:maybe a nitrogen deficiency? try fertilizing.