Confidental Transactions or Coinjoin would not help him to get more privacy if he keep reusing the same address again and again !
Do you even know how CT is supposed to work?
The transferred ballances are hidden to the public, but the adresses are publictly available. If you reuse one address, how can it help your privacy much when using Confidental Transactions? We wont know the final ballance is exactly 4000 Bitcoins, but we still could trace all OKCoin transactions and estimate final ballance pretty well in this case.
The first step to more privacy is stop reusing the same address again and again. Sorry if it hurts your feelings how you use Bitcoin.