I had the same experience the first time I used the ammo lock. i had bought it because I had a few ottos die and they are sensitive to ammonia. I knew that ammolock turns the ammonia into ammonium.
Next week I used the ammolock instead of the stresscoat for my weekly water change. All the fish were at the surface gasping next morning and I went thru a mini cycle. I was absolutley distraught. i spent hours on the phone with companies that make dechlorinators and they basicaly said I had done something wrong.
Perhaps i did, perhaps I didn't. They said i cleaned my tank too good and probably killed my bio filter when i vaccummed the gravel and washed the fluval sponges at the same time. now I don't do filters the same week i vaccuum. i alternate weeks.
Please be aware that if you have chloramines you will get ammonia after using the ammo lock. That ammonia is non toxic( ammonium), but your test kits will register it as ammonia. if you can get a test kit that is an acetacylic acid kit it is supposed to be able to register the difference. i can't get the kit here-- no-one will order it for me.