The trick with direct off solar, no battery, is to keep the inverter happy. If the pump draws a hit of current when it starts, and that causes the DC on the inverter's input to sag too far, because the solar charge controller will have some sort of response time, the inverter will likely go into low voltage shutdown.
A decent amount of additional capacitance on the inverter's input will usually hold things up well enough if that proves to be a problem but unless the pond pump is quite low power, IMO, a single 250 watt panel isn't going to cover being able to start the pump for a fair bit of the day, but once started it might do the job. It all boils down to the ratings on that pump.
