I take Solgar chelated manganese. When I started I had elevated liver enzymes and was told to start very low and go very slow. I started with 0.5 mg/day, worked up to 0.5 four times/day, then increased the size of the dose.
At one time I was taking 8 mg twice/day. I was getting a 'twinge' in my right side that I thought might be my liver so I switched to 4 mg four times/day. I took that much from only 3 months. The Institute of Medicine sets the safe upper limit for adults at 11 mg/day.
WaterOz makes a liquid manganese that I have seen recommended.