Ammonia Spike in Aquarium

Question
Hi Nathan,

I am hoping you can help me.  

I have a 40 gallon freshwater Aquarium that houses 2 common Goldfish.  My aquarium is up and running nearly 3 years.  My PH is 7.6, my nitrite is zero, my nitrate is between 0 and 5ppm and usually my ammonia is zero but at the moment my ammonia is between .5 and 1.  I am not sure what has caused my ammonia to spike.  It happened about 4 to 5 weeks ago.  The only thing I can think of that may have contributed to the spike is that I washed some of my ornaments within the aquarum as they had algae on them so I scrubbed them under tap water and perhaps I got rid of some very beneficial bacteria.

Since the spike about 4 to 5 weeks ago, I have been doing partial water changes every couple of days.  I have also just recently bought myself a second filter, an external filter which I set up last Friday.  I was told having a second filter and particularly an external filter would greatly improve things overall.  

My question to you is, why isn't my ammonia reducing?  My aquarium is more than adequate in size for 2 Goldfish - it means they have 20 gallons each.  Before the ammonia spike I did regular weekly water changes and I never had any problems.  I can't understand why the ammonia is not reducing at all.  Is my tank cycling all over again?  What can I do to help the situation?  

By the way, both of my Golfish seem fine and have been fine through the ammonia spike to date but I still want to rectify the situation as quickly as possible.

One final thing, I have used a couple of ammonia reducing agents like Ammo-Lock but I really want to keep away from them.

Answer
Hi Katie,

You fishkeeping routine and habits are perfect - keep up the good work!

Your ammonia spike probably happened because you destroyed some beneficial bacteria in your tank. You could have done it through multiple ways:

-Changing out all the filter media in the filter
-Changing out the cartridge in the filter*
-Cleaning out too many items in the tank
-Performing more than a 40% water change
*Filters that use a cartridge are not very good, because all the beneficial bacteria get destroyed when you change it out (except the Bio-wheel ones)

I would do a daily 10% water change until your ammonia gets under control. Fortunately, your Goldfish will not be impacted much by 0.5-1 ammonia, because they are amazingly tolerant. If you do the water changes, there's almost no risk to your fish. Just don't do anything more than a 30% water change, because that risks losing much of the bacteria. Don't change ANYTHING in your filter at this point.

My estimate is that it should go down in 1-2 weeks at most, if you keep doing water changes, and not disturbing your filter.

Good Luck, and Best Wishes to you and your fish!