If the ammonia is .25 ppm even after a water change, then there is a problem. While a large % of it is in the less harmful ammonium form, even this is not benign. You definitely need to do something about it.
If you stop adding nitrate (fertilizer) the plants should increase their use of ammonia as a source of nitrate.
I would not add Excel or the generic form while you are still trying to grow nitrifying bacteria.
If you want to add more of the right species of bacteria look for Nitrospira on the label. All other 'bacteria in a bottle' products have the wrong species of bacteria.
If you stop adding nitrate (fertilizer) the plants should increase their use of ammonia as a source of nitrate.
I would not add Excel or the generic form while you are still trying to grow nitrifying bacteria.
If you want to add more of the right species of bacteria look for Nitrospira on the label. All other 'bacteria in a bottle' products have the wrong species of bacteria.