I borrowed a coolant leak test kit from my local auto part store. With the coolant at ambient temperature, I pressured the coolant system up to 18 psi. I noticed a small drip at a hose and another small drip on the back side of the water pump. Both were very small leaks, about one drop of coolant was leaking every minute. Even with the small leaks, the system held 18 psi for 10 minutes. After 10 minutes I depressurized the system. Next I checked for compression and combustion leakage into the cooling system with the pressure test kit while the engine was on. The system held pressure with the engine on and the gauge indicator did not oscillate. I tested the expansion tank cap and it leaked air rapidly. So I'll get a new cap, torque the water pump so to better seal the o-ring, and replace the leaking hose.
I am surprised the stop leak tablets did not seal the small leaks I have in the cooling system. I have plenty of stop leak in the system. When I drain the coolant, I can see the small stop leak particles in the coolant.