In short it removes virtually all that is harmful from the water.

That process can be divided up into 3 methods: the BIOLOGICAL, the MECHANICAL, and the CHEMICAL, of which the biological is the most important technique enabling you to keep your fish alive.
The basic idea behind the BIOLOGICAL filtering technique is the growth and the maintenance of bacteria that consume the ammonia created when ...erm...fishy wastes...dissolve into the water.
The bacteria can be established on any filter media - gravel, sponge (not your household sponge ! - they often have bacteria inhibitors), filter floss or any other special material that is safe to use in the tank. The process of growing a bacterial colony is easy enough, but requires a bit of patience

DON'T BUY THE FISH WITH THE TANK !

Position the tank on it's stand, plumb in the filter, fill the tank with water, lay out the plants, rocks or whatever appeals to you (and which is safe for the fishes - does it dissolve and poison the water ?) and then put in a couple of pinches of flake food and switch on the filter - you want the food to rot to create ammonia for the filter bacteria to live on.
Remember that from now on the filter power will only be switched off for very short times (10 - 15 minutes ideally) such as when you want to clean the filter. This is because you are breeding OXYGEN breathing bacteria. Cut off the water flow and the bacteria will soon use up the oxygen in the surrounding water and then start to die.

KEEP THAT WATER FLOWING !!

Now all you have to do is to leave the tank alone for 3 weeks Remember: don't turn off the filter, just add a bit more flake food every four or five days. To be on the safe side, I would purchase 2 water testing kits. The ones you want are for testing the levels of AMMONIA and NITRITE. Both substances are lethal to Goldie, so you want to make sure that there is nothing of either in the water ie: that your filter bacteria are consuming all the ammonia and nitrite that you are creating by allowing food to rot in the water. Maybe do a test on the water after the first week, just to see what the test results should not look like - and then a test before you go out to buy your fish (At this point there should be no ammonia and no nitrite - Goldie will be stressed out with travelling and vulnerable to disease so give him the best conditions you can). Once the filter is up and running with zero ammonia and zero nitrite, you only need to test around once a month, just to keep a check on things.

If you have had a major power-cut lasting 3 hours or more then the test-kits should be used each day, combined with a partial water change of 25% of the water, if needed, until the ammonia/nitrite readings are zero again.

I mentioned cleaning the filter: well the idea is to NOT use soap, hot water or any other cleaning agent. They are going to kill ALL the bacteria - what you actually want to do is to wash away a portion of the population (to make space for more new ones to grow) along with whatever gunk has got trapped in the media.
You merely drain some of the water out of the tank into a clean bucket (it's a good idea to keep one just for the tank - no prior use of detergents etc therein), and rinse the filter media out in that.
Ideally you should also only clean half the filter at any one time - this allows the other half to continue to function, thereby keeping the water safe. It is also a good idea to put the unwashed media before the washed media in the water flow in order to speed up the bacteria creation in the clean media. The actual period between the cleaning sessions vary tremendously: What kind of filter are you using ? How many fish do you have in the tank ? What do you feed them ? The more sophisticated filter powerhouses like the cannister filters can go for a month or two before needing to be cleaned (my own cannister gets looked at only every three months, but it is big with a great deal of filtration area). On the other hand a simple air-driven sponge will need servicing about every one to two weeks.

The MECHANICAL process is pretty simple. Effectively you bung some form of filtration media in front of the path of the water, allowing it to drain through leaving behind any particles that it was carrying. The actual media vary from the basic gravel to some fancy artificial shapes. What you use will depend on the type of filter: a simple cylinder of foam does the job for the basic filters, while my cannister has hexagon shaped bits as a pre-filter to catch the bigger bits, and then a specially shaped foam circle for the smaller elements. How often you clean out the mechanical media also varies - I check the water flow coming from the filter as a guide (easier to see when some water has been removed): when the water flow seems to be about half of that of a clean filter, then I start the cleaning process. The professionals say that this should be done around once a week to prevent the mechanical media becoming biological. Me, I don't have that sort of time, so the small filter gets looked at when the water flow is reduced to half, and the cannister mechanical media gets done at the same time as the biological - every 3 months, and all my fish seem happy, hungry and healthy (remember to always leave half of the biological media untouched - you need to keep a colony of fully functional bacteria to avoid ammonia/nitrite problems.



Measure out the halfway mark up the tank side, taking from the top of the gravel up to the top of the water as the top and bottom.
Then find the middle of the upper half and make a mark, just by the side on the glass with a permanent pen. This is handy when doing water changes as it gives you a fairly good idea how much 25 percent is.

The CHEMICAL filtration removes smells and other dissolved substances from the water - very useful for taking out medicines after treatment. The media normally used are either carbon or zeolite. The main snag with both is the inability to judge when they have adsorbed as much as they can. I would recommend using them for a specific purpose, and then removing them. Zeolite is primarily an ammonia remover, and as such is useful when first starting up a tank to avoid any ammonia peaks. It can also be recharged by soaking in a very strong salt solution overnight and then rinsed well to avoid putting salt back into the water. Zeolite does not remove ammonia in salt water.
Carbon takes out medicines and smells, and kinda scrubs the water making it sparkly clean ! But it has a limited lifespan and cannot be recharged, so I don't use it continually. It will last for between 2 - 3 weeks, depending on the bioload. Go to top of page.

A filter does 3 things

• Mechanical Filtration
• Chemical Filtration (Optional)
• Bio Filtration

Mechanical filtration (wool/sponge) removes wastes and excess food.

Chemical filtration e.g. activated carbon/zeolite removes organic compounds/medications

Bio filtration (biohome, bioballs, ceramic rings) removes ammonia, nitrite and sometimes nitrate. Benefical bacteria (BB) can be found on all solid surfaces. Specialised bio-media are used as they have a larger surface area to allow more BB to grow on.

:banana:

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