Point it at the rocks to disperse the flow.
Did it come with a variable power supply? Or, is there an option to buy one, in which case you could get one and turn the power down.
Put it on a wave mode, as it'll then only be on the highest flow for part of the time.
Put some netting over it to reduce flow (side benefit to protecting it against a nem or other things getting stuck in it).
Swap it with someone for a smaller model.