This may be a RAM issue. I don't see why the phone is using up RAM even when it is not in use. Follow this step by step process that may help you resolve the issue:
1. Power the phone off, then power it back on.
2. If the problem is not solved, try plugging the device in and charging it to 100%.
3. If it still is not working and is closing apps and running slow still, it may need a RAM card replacement. Just go online and look for a place that sells RAM replacement cards for the Blu Studio HD 6.0. That may solve the issue.
Hope that helped!