08-02-2012, 02:09 PM
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if you changed the filter cartridges then you removed a lot of the good bacteria living in your filter cartridges. This disrupted your cycled tank, what you are now experiencing is likely a mini cycle. Its not uncommon to have a bacterial bloom in the water during this time. However the minicycle is dangerous and can easily be life-threatening to the fish in the tank. The filter pads are more or less the heart of the tank once they have established a good population of bacteria on them to handle the fishes waste, establishing the bacteria on the filter pads takes time and without them the waste builds up poisoning the fish. Your best bet now is to get a test kit and be ready for daily water changes until the tank is able to establish the filter again. Typical rule of thumb is you rarely replace filter pads/cartridges in a tank, simply clean then in old tank water and reuse them. If they need to be changed you should do only one at a time or run the new and old pad together for a few weeks before removing the old one.