Maintenance

1) WATER QUALITY
Water quality is the overiding factor that could mean success or failure in this hobby. The more seasoned among the enthusiasts will tell you...'take care of the water and the fish will take care of themselves'. Of course lets not take the old adage at face value. You will still need to feed the fish, do regular water changes and clean out the filter and tank, etc, etc.

a) Water changes
Ok. You've set-up your aquarium already. It's been running for the past 2 months without any problems. You added your goldfish at the 5 week mark, after you cycled the tank of course. The fish seem to be doing well. They look good and are eating well. It should be smooth sailing from now on right? Well...right...provided you exercise some discipline in doing a few critical tasks, one of which is regular water changes.

A 100% stocked (meaning that you have a 100Gal. tank and are keeping 10 goldfish) tank would require 10-15% water change every week. But that's the figure given by fellow enthusiasts in colder climates. Here in the tropics, More frequent or larger water changes will be necessary. Goldfish tend to eat more and produce more waste when the water temperature is higher. Personally, I do a 40% water change every 6 days so. I've found this to be the ideal schedule considering the limited time I have to tend to my fish. Also, it would help if you have a large volume filter. Larger filters can keep a larger and more stable colony of bacteria, and clean your tank water more efficiently and quickly too. If you have the time, 20% water changes every 3 days would be even better.

If you have an outdoor pond, the sunlight will encourage the growth of algae. For some goldfish experts, algae in the water is actually a preferable condition to raise good quality specimens. However, the algae will tend to cloud the visibility of the water and ruin the aesthetic quality of your pond. To prevent algae, the addition of salt would be beneficial. In fact, goldfish tend to thrive in slightly brackish water. Salt also prevents the growth of parasites and other undesirables. Alternatively, you could install a UV Filter to prevent algae. They work by exposing the water to UV light and causing the Algae to clump together and be trapped by the mechanical filter.

b) Cleaning the Filter
Never clean the filter in clean water, even if it's declorinated. Always reserve a part of the water removed from the tank in a bucket. Use that water to rinse out the filter media. Never ever clean out the filter too rigorously. Remember that if you do that you will also be destroying the 'good bacteria' that has taken so long to be established.

If you need to replace any of the filter media, try to replace only 50% of it at any point in time. This is to ensure that some of the 'colonised' filter media still remains to 'seed' the new filter media.