The tank may be a small accumulator tank and by letting the air out of it you have defeated the purpose. Drain the water...close any valves and try again.
You may need to prime the system by filling the feed hose to the
pump with water and elevating it above the
pump. Turn OFF the water input to your hot water heater to eliminate that as an issue. Start with all faucets off and open only the closest one to the
pump first until a nice steady flow with no air is present. Then close that and move to the next faucet etc. etc.
Do this ONLY with the cold water side. Then move to the how water side and repeat with the valve to the hot water heater open.
Of course it is possible that you are sucking air on your intake side but try the easy stuff first.
Good luck!