It sounds like it was loosing it's prime and regaining it (self-priming pump, right?)

When things cool down (man and machine grin ) take the connections apart on the suction side and make sure all the dirt and grit is out of them. I'm assuming that they are the banjo quick disconnect fittings? Are all the gaskets in place?

I had the same problem, and it was sucking water so fast that it created a vortex, letting air go all the way down to the hose. I ended up slowing down the pump to reduce the size of the vortex until I got the water lower.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).