Why am I seeing in-application balance decreasing after I switched the toggle off?

You might see the balance changing within 24 hours after switching the Speed Increase toggle off. This happens because, when you bid on a piece of data, your BTT goes to escrow first and stays there until you complete downloading the piece or until 24 hours passed – whichever comes first. If the piece was successfully downloaded, your bid goes to the seeder. If download was not complete, BTT from escrow will be transferred back to your balance.