I'm not sure if you remember but I had an ap600 a few years back and it did the same thing. Obviously, it shouldn't because feeding messes with the surface tension of the water so the foam should fall flat. The fact it doesn't makes me think that the skimmer material leaches some chemical very minutely that makes it go crazy when you feed. If I remember correctly, that isn't cast acrylic they are using. I think people said it was extruded but even that could be hearsay. And even if its extruded, we still have no idea where it came from Mexico, India, China, German, U.S., who knows. The issue being the manufacturing level of quality for the plastics. In some situations cheaper materials (materials not held to the same standard) aren't a bad thing and in others they are.
Deltec has a great name (I love that name) and great advertising, that have (or had) great support but the materials they use look cheap. To be specific, if you take the pump off and compare a similar sized deltec skimmer body to a mtc skimmer body, the mtc probably cost at least twice as much to make.
