^ my guess would be as follows:
1) you may have caused your Beneficial Bacteria to crash when you accidentally cleaned out the filter...
2) Then adding to the fact you have some large fish producing a lot of waste your filters are having a hardtime building up the BB needed to convert the ammonia to nitrite, especially with a Ray in a 75G tank...
Considering rays are some seriously high waste producers.,.
3) adding stuff like accuclear is just binding smaller particles together so they can be more easily trapped in your filters which at the end of the day could also be filling your filter media with quite a lot of gunk meaning its not filtering properly...
So with that being said, i would probably do the following;
1- keep up with small daily water changes
2- stop using Accuclear (its like a bandaid on a knife wound) you need to fix the problem...
3- Maybe even consider thining the stock a bit, coz as your current occupants grow, the amount of waste produced can only grow with them, further causing problems in your tank unless you stick with a religious water change schedule to keep up with them...