So how do you prevent your tank from siphoning back through the pump when you shut the pump off?

I don't shut of the pumps when feeding, my fish have just gotten used to it. Even with my corals I keep everything running.

Shutting the pumps off for feeding, power outages, whatever, should design your system to handle what might return to the sump.

I like that theory. That's my excuse for leaving the powerheads on. Even though I have the auto shut off feature (Tunzes) I don't like to be controlled myself, that way. I'll feed 'em when I'm ready to feed 'em, not when the controller is ready. Too lazy to unplug them manually, each time. However, I should augment this by saying that I do have high NO3 and I probably overfeed. Working on both.

I never target feed my sun corals. Have 5 of them and they are all doing fine. I feed Cyclopeeze (freeze dried and frozen), Coral Frenzy, and Live Rotifers. (Not all each night). Because I leave my powerheads/pump on, the stuff gets blown all over the place. Sun corals open up everytime this food goes in. Actually, they begin opening up when I first feed the fish mysis, plankton, squid, Marine Cuisine, Emerald Entree (whatever the flavour of the day). They sense it and I suppose there are enough little bits for them to chow on. Then they get the other micro foods.

I keep my flow going as well. Only have several corals that don't require target feeding. My fish don't mind chasing the food. I figure when I'm away for a few days, no one will be there to turn the pumps off and on at feeding time so they may as well get used to one mode. I let my auto fish feeder do its thing even when I'm at home, only difference is, I feed frozen goodies in the evening manually. The feeder is an Eheim double barrel model with flakes in one compartment and CycloPeeze granules in the other. The routine is flakes in the morning, granules around noon and the frozen goodies in the evening. Yep, 3 feedings a day but each one is a light feeding. So the only difference to the critters when I'm not around is the frozen stuff in the evening, they'll end up with more flakes from the auto feeder. Almost forgot, I also provide a small amount of nori on a clip for the tang & angelfish I have. Pumps have no effect on that of course.

In order to prevent all the flakes from ending up in the overflow for my skimmer, I fashioned an acrylic mount for the auto feeder with a kind of box affair extending into the water to act as a feeding ring. This allows the flakes to soak a little so that they sink instead of floating away on the surface. The Singapore angelfish and cleaner shrimp often come along and help flush the food out of the holding box. Once in the water column, the flow nicely distributes the stuff so everyone gets a crack at it. As far as I can tell, they enjoy the hunt.

I think it depends on WHAT you are feeding... For instance... When I feed mysis, I turn the pumps and powerheads off so food gets down to all the critters, but when I feed BBS, I leave powerheads on and just shut off the skimmer (sumpless) so that the BBS is always moving around, not just sitting up at the top where the light is.

I run everything 24/7. I don't even bother to shut my skimmer down to clean the collection cup, dial it back pull the cup and off I go.

Same here.

The tank water siphons to the sump (fills it 3/4) until the water level goes below the outlet from the tank which stops the siphoning.

I want to add I also remove the sock filter and put it back on in the evening. This allows any microfood to cycle back into the tank rather than getting caught up in the filter or the skimmer which I also turn back on at that time.

Good advice. In my case, my sump is big enough to handle all the water that my tank will return through the pump when it is shut off. But I also have a check valve in the line that only allows the water to drop to the overflow boxes. That way, the water in the display tank only drops about 1" with pumps shut off. BUT, if the check valve fails, the sump can still take all the water...

I shut off my return pump for feedings, but leave the closed loop running. This tends to circulate the food to all the critters. Reefkeeper 2 is adjusted for a 10 minute delay. By then, every morsel is history...