Whats the nitrates of the water you use from the faucet or where ever you get it. ???
I don't think a nitrate reactor is necessary there is a reason for the high nitrates, we need ot locate it.
If your tap water is low in nitrates then something is rotting in the tank and/or your gravel is mighty dirty to have nitrates that high.
You need to do 50% water changes.. I would do 2 50% water changes this week. One right away and another in 3 to 4 days..
you have 2 filters I would scrub them each. Do one with the 1st water change the next when you do the 2nd. Clean the medium in each filter, and or replace it it is looking rough and unclean-able. Just do not do both filters at the same time. lots of beneficial bacteria there and you wouldn't want to reset your tank by doing an overzealous cleaning of your filter medium
You have some cory cats but I would look into another bottom dweller scavenger to work your tank