[Delphinus]

Sorry, I forgot to mention this earlier. I actually recommend AGAINST a check valve.

It will work as a temporary solution but it's not good for a long-term solution. They put a lot of back pressure against the pump so you will lose a lot of flow. But more importantly, as your pipes will inevitably get that slime coating buildup on the inside (because you're not pumping sterile water), the seal will fail, and water will backflow through the check valve anyways. And that's not including things like getting a little bit of sand, or a small snail shell or whatever, stuck in there ... potentially one very big mess on your hands.

Also (maybe not as important) but sometimes check valves can be very noisy, depending on how bad the flapper valve inside rattles around in flow conditions. EmilyB had one that was so loud it sounded like a jackhammer.

It's really only a temporary solution ... you can try it, but if it were my tank, I wouldn't. I did this for a while on one of my tanks a few years ago and I found out the hard way that they can fail .. and I'm not interested in cleaning them out every week. Plus, after I took it off .. I couldn't believe how much flow came out of my sump return. It was as if I had added a second pump or something ... that check valve put a LOT of restriction on my sump return.