Ammonia spike after water change?

Today I did a 50% water change and, as usual, treated the tank with a double dose of Prime before refilling the tank. I noticed afterwards that my SeaChem Ammonia Alert showed a positive ammonia level. I double-checked the result with a Mardel ammonia test strip which confirmed the result. The ammonia level is now returning to normal. I am assuming the ammonia spike is due to mulm at the bottom of the tank being stirred up during the water change (although I do my best not to stir things up too much). I do not want to expose my fish to any appreciable ammonia levels. Is there a trick to keeping this from happening? How hazardous is this to my fish? Since my plants are doing so much better (i.e., not rotting away), there's not much stuff to vacuum up. Any ideas appreciated.

 

It must be the chloramines, then. I use Prime dechlorinator and I go through a 250 ml bottle in about a month and a half (I have a 55 gallon and a 5 gallon tank). I just did the tap water test and got a slightly higher result (1 ppm) . Our water authority does add both chlorine and chloramines to our water, in such large quantities that our LFS recommends double dosing dechlorinator, particularly after heavy rains. I will not worry about it unless the ammonia level does not drop to zero in 24 hours. Thanks for the help.

 

You're right, the last 4 months is probably not a good indicator of future use. I had three other tanks (they're gone now) plus a quarantine tank (not set up right now). I also used up a bunch of Prime when I converted this 55 gallon to a planted tank, due to a substrate issue which required me to drain the tank--twice--and move all the livestock into a 20 gallon for two days. Finally, I am getting to the point where I can actually start to enjoy the fruits of my labor!