Gardenia Leaves Turning Brown?

I have a gardenia tree which I move inside during winter as it's in a pot. This is the second year I've had it. Some times blooms and has nice flowers, but at times I get brown spots on the leaves. I don't know what is the cause. Some say it's the PH and some say it's the water or the light. It has sunlight for about 3 hours then bright light the rest of the day. I'm attaching a photo of the leaves with the brown spots. Hopefully, someone can identify that. I checked for pests there aren't any.

By lahib