Howdy,
There were some excellent questions, the best came from DeLgAdO

: Your pH value is the pivotal point, since it directs the equilibrium between ammoinia and ammonium. With 0.25 ppm total NH3/NH4, you are still safe. Once it hits 1 ppm or once your pH value rises above 8 you are in trouble (or rather your fish are in trouble).
However, you should do something about it, since your tank seems to be on the edge. Your filtrations
sounds good, yet, I still believe that this is where your problem is. High ammonia means nothing but a) decaying biomaterial in your tank or b) insufficient biofiltration. I simply assume that you remove excess food and dead plants on a regular basis. Therefore, I rule out option a). It might be your filter maintenance. Maybe you clean your filters too often and, thus, prevent bacteria from reaching full capacity?! Try bottled bacteria again as if you set up a new tank (bottle instructions). Also, leave your biomedia alone for several weeks/months. Did you maybe use meds that killed your bacteria?
Also, plants are your friends

No need to prune healthy leaves off. However, you should remove any detritus from your tank.
Good luck,
HarleyK