Even though you are on the same aquifer, there may be points were due to agricultural runoff, or even lawn fertilizer use, where nitrate spiikes may concentrate.
When I interned as a water supply tester, one well near a feed lot could have drastically different results than a neighbor upstream of the other side. And one persons over use of fertilizer or leaking septic bed be noticeable. There is an often small cone of depression where water in one well is collected, compared to one only a small distance away influenced by bedrock, sand or other substrate.
Sounds like you created a new mini cycle with the change.
If it were me, I;d cut back on the feeding, and try and dilute the high ammonia water with lots of partial water changes.
When I interned as a water supply tester, one well near a feed lot could have drastically different results than a neighbor upstream of the other side. And one persons over use of fertilizer or leaking septic bed be noticeable. There is an often small cone of depression where water in one well is collected, compared to one only a small distance away influenced by bedrock, sand or other substrate.
Sounds like you created a new mini cycle with the change.
If it were me, I;d cut back on the feeding, and try and dilute the high ammonia water with lots of partial water changes.