Auger, I did the same thing once, got some from the beach here. They lasted for a while until some of the crabs and fish found them and started eating them. They looked real close to the same ones as IPSF sells. I think the only difference is that the ones we get from our beaches are in colder water and live in more of a mud vice sand. IPSF clams are in warmer water, hawaiian waters.
Charlie, my amonia problem was from a water change, not the clams. Long story but I used some NSW that I had grown some pods in, amoina was way high and I didn't check it until AFTER I did the water change. Found it and threw out the NSW I had left and went and got more NSW to do a massive change. Unfortunatly, the damage was already done. Luckly, I only lost my sand bed critters and some sponges, all of the corals and fish made it.