Im changing water like the hoover dam. 3 rays in my temp holding 90 gallon while the new 230 cycles. The 90 has been running for over a year on the same filter no issues.
3 6" rays. It was on the highest end of the scale on the test.
What size water changes have you been doing? When cycling my 120 I would take out 30 gal and that was a great cure all. When you do your water changes do you stir up the water and try to get out all the waste that has gathered on the bottom. Poo and old moldy food can always lead to disaster. I wish you luck. Like I said I would always change out at least a quarter of my water. Stir up the waste and get it out. If that does not work they make all kinds of products that will remove it. Maybe another member can help you there seeing as I have never bought anything like that.
Ammo chips are the best way I know of to save the fish inhabitants during an ammonia spike. A healthy tank should not need chemical filtration like ammo chips but they a great way to deal with the symptom of an ammonia spike while you find and rectify the underlying problem. I also like that the ammo chips peter out over time. As they loose effectiveness the bacterial colony is able to reestablish itself without killing off all the fish.
If the ammo chips help bring it down, I would still do very large water changes - like 45 gallons/day. Maybe with the chips you could do 30 gallons/day but you can sort out the amount once you've taken these steps and test the level each day to find out where you are with the ammonia levels.