sudden tank tragedy

Question
Hi Nathan,
I have had this 50 gallon freshwater tank for 3 years.  I use a Marineland Penguin 200 with a biowheel.  I change the charcoal filter and do a 25% water change monthly. Two weeks ago I had to move the tank, so I did an 80% change, refilled with water and added Aquasafe to the new water.  I have done this before with no problems.  The fish I had were 2 tinfoil barbs(4") 4 pictus catfish (3") 1 silver dollar (2") 1 upside down catfish (3") and a small plecostomus. My tank seems to always have perfect levels so I get complacent with my testing.  Yesterday I was not home and didn't look at my fish.  This morning I woke up to all of my picus cats floating and my silver dollar swimming sideways.  The barbs looked awful...velvety, listless, cloudy eyes, swimming at the surface.Not really thinking clearly,I quickly did a 50% water change before testing.  Now all fish are dead but the pleco.  I tested (after the water change): Ammonia: .50  Nitrate: 10  Nitrite: 0  pH:7.6.  
How could the ammonia get so out of control?  
How can I tell if the filter is not working?  The water is clear and does not smell(even before the water change).
What steps do I need to take to get the ammonia down and to get ready for new fish?  The 1 pleco is hiding now, but it seemed fine earlier.

Thank you for your help,
Mary


Answer
Hi Mary,

The reason why the ammonia levels went up is because the beneficial bacteria which remove toxins were eliminated during the move. You probably took out the filter, and emptied out the water. The filter cartridge and the Bio-Wheel most likely dried up to some degree. If the beneficial bacteria are exposed to air too long, they will die, and this is probably the most likely scenario. Without the bacteria, your aquarium cannot control the ammonia.

It's not the filter's job to remove the ammonia, but rather, the beneficial bacteria living within it. So, the answer to your question "How can I tell... not working?", is if you don't see any water coming out, then it's not working. The beneficial bacteria takes time to establish (cycling process). The cycling process is the process in which beneficial bacteria are established in your tank. You will have to start the cycle over again. To get the ammonia down, you can do daily 10% water changes. Right now, perform a 30-50% water change to get rid of some of the ammonia, to make it safe for your Pleco. You can also buy a ammonia-removing chemical at your local fish store.

Then, add a few fish (max 6). These are hardy fish that will get your tank through the cycle. The 'cycle' takes one month approx, and DON"T add fish during this time. After the month is over, you can add more fish, about 2-3 per week. During the first month, perform 10% water changes every 1-2 days, to keep ammonia concentrations down.

Good Luck , and Happy Fishkeeping!