I didnt read all 4 pages of thsi thread, so someone may have already said this but i wouldnt add any more filtration to your sump. Adding in new media can cause the cycle to start again.
I would just keep up with the water changes and prime. My opinion is your going thru anotehr cycle.
Your media was not cycling that much bio before with just a few fish in it.
Now that you have the rays in there, your bio is larger and the system is going thru a cycle.
it could take up to a month to fully cycle and settle down.
No amounts of Ammonia or nitirites are good in the tank.. so you should at least for a 30% water change daily or do a 45% water change every two days.
I would rec a daily water change.. this will help keep the ammonia and Nitirites down low and there for keep the rays in better health.
Feed daily, skipping one day a week.. Feed just a little less than normal to help keep the bio load down. Also take out any food that is lect after 10 min.
This should help.
I figured, if your ammonia is that low and your nitirites are also low, your cycle should settle down in about 2 weeks. Keep an eye on your Nitrates also so you can see what steps your cycle is going thru.
Hope all the advice everyone has given helps. It was caused due to the tank was still new and not cycled with a higher bio-laod before adding the rays.