My advice is the same as Murat. In Baja we have the best luck by diving down into the rocks and not moving. The grouper out here are not shot at alot but they are still real easlily scared. I make almost all of my shots from the bottom on my stomach aiming at a slight angle up at the fish as he comes over to check me out just above the rocks.
They are for sure a stalking fish.
I dont know about tanks though if the technique is different.
Never try to swim right at him or chase him down.
GTB
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