Fish keep ending up in the filter!

[greenhat06]

Hello all. I recently un-stocked my fish tank and then re-stocked it. My previous fish had been dying because they were all community fish mixed in with a larger Red Tail Shark. I have a 30 gallon tank and a Marineland Filter (I believe it is 200 gph, but not positive. I can check if necessary). Anyways, I took every single fish remaining out of the tank and decided to start fresh, except leaving the Clown Pleco in there (roughly 2" long). I bought an electric blue ram, as well as 8 Rummynose Tetras. That is it. This was two days ago. Yesterday, I only counted 7; when I unplugged the filter, out popped one of the little guys, curled up like it had been stuck in there. Then today when I got back from work, I only counted 6. Again, curled up from being sucked by the filter. I have NO idea what is causing this?! My most recent water levels using API MK were:
Nitrite 0
Nitrate 20
Ammonia 0
pH 7.4 - 7.6

Any ideas?? It is my understanding that as long as the fish are intrinsically healthy, there is no reason for them to be getting naturally sucked up by the filter? I mean, the tubing for the filter doesn't have any sort of "protection" on the end to prevent it sucking up the fish and only allow water through, but again, I am under the impression this would be unnecessary if the fish are healthy. I ordered a thing of Seatech Primer and it arrives tomorrow. What type of water changes and addition of Primer do you recommend? Or what to do!? I can't keep losing these guys, I need a stable tank