Why do ammonia levels spike after water change?
Tap water often contains ammonia or chloramine (which is chlorine bonded to ammonia). Products like Ammo-lock and Aqua Safe convert ammonia to non-toxic sister chemicals, but the neutralized ammonia still shows up as ammonia on test kits that use Nessler’s Reagent, which includes the majority of hobby ammonia test kits on the market (I’m omitting some chemistry here, but that’s the general idea). This neutralized ammonia will be broken down by your filter bacteria, the same as ammonia would be. So, even though it looks like you have more ammonia when you use a test kit, the water is safe, and your fish will benefit from the water change. By the way, if you have pieces of leftover food lying or floating around in the tank, and it’s been more than five minutes since the last feeding, you are surely overfeeding your fish. This can cause ammonia problems in and of itself. Feed no more than the fish will completely consume in three minutes.
