Your nitrate should really never read 0. That's why we are guessing your tank is not cycled. Two weeks is probably not long enough to cycle a new tank. Did you reuse media from old set up? With these fish why would you go to a smaller tank? Also how do live feeders get stuck in the filter? Seems more of an issue for uneaten non live food.
I reused the media and canister from the old set up so I'm not sure why still need to cycle tank for so long. downgraded because it cost me way to much to maintain a 6 feet. I will upgrade again as they grow. Now all 3 of them are only at juvenile stage. I'm aware that Rays and aro need large tank as they grow so I will upgrade a year later when I move house.