Aquatics Unlimited: Articles: False Ammonia Readings
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False Ammonia Readings

for the week of 9/17/98

Once the first week or so of the Break-In Cycle is over, any ammonia readings higher than zero are cause for concern. Since even trace amounts of this toxic waste product can cause both short and long term damage to fish, some hobbyists routinely test for its presence. Unfortunately, in a couple of common instances, ammonia test kits can give false high readings, causing the hobbyist unnecessary worry, and sometimes resulting in action (such as massive water changes) that cause undue stress on the fish.

One common cause of false ammonia readings is the test kit itself. All kits are not created equal in the first place, and some appear to have much longer shelf lives than others. In our experience, ammonia test kits with sealed packets of pre-measured powder reagents generally are quite accurate and have a long shelf life. Liquid reagents follow, then bulk powder, and finally tablets. A few kits have expiration dates on their reagents, but most do not. If you have reason to suspect your kit is more than 6-12 months old, have your readings verified by comparing with another kit, preferably of another brand, before taking any drastic action. Interestingly, outdated ammonia test kits appear to give false high, rather than low, readings.

Another common cause of false high ammonia readings is the use of ammonia-binding chemicals such as Aquarium Pharmaceuticals' Ammo-Locktm, and Kordon's AmQueltm. These products and their byproducts cause high readings on test kits which use the Nessler method, which is unfortunately almost all the popular sets. A Salicylate-based kit would need to be used to determine true ammonia values in tanks containing ammonia-binding agents.

True high ammonia readings are not common in established aquariums, and even less common in those that are well-maintained. If your test kit shows "toxic" levels, but your fish look fine and dandy - don't panic! Get a second opinion.

"Tip of the week" appeared regularly in 1999 and 2000.

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