Choosing a filter for your Goldfish Aquarium
After tank size, filtration is the most important equipment choice when it comes to keeping goldfish.
A filter keeps your water clean, and not just in a ‘my water is clear’ sense. Inside a fish tank filter biological reactions take place converting waste and toxins in the water into the less harmful Nitrate.
The two main types of filtration that occur inside your filter are mechanical and biological filtration.
Mechanical filtration involves filtering particles out of the water column via sponges. Sponges are available in different varieties of fineness depending on the waste load produced by your fish.
The more coarse the sponge used the smaller the particles that will be able to pass through it. Likewise the finer the sponge more debris will be picked up but the sponges will require cleaning more often.
Biological filtration is the process of bacteria breaking down toxins in the water.
There’s already a million articles on the internet about the Nitrogen cycle so I’ll just touch on it briefly. In an aquarium, the fish, leftover fish food from feeding and any plants you keep produce waste. Fish produce waste via feces and urine and plants produce waste via dead or rotting debris. Even if your plants are healthy they will still at times discard plant matter which winds up being waste that needs to be broken down.
Essentially any organic matter in the aquarium that is not living will begin to rot and be broken down into toxins that need to be filtered.
The first level of waste in the aquarium is Ammonia, the second is Nitrite and the third is Nitrate. NitrITE and Ammonia are both toxic to fish and this is where a filter comes in. Naturally occurring bacteria can inside a filter and will convert Ammonia into Nitrite and then NitrITE into the relatively harmless NitrATE.
This bacteria will colonise the inside of a fish tank but work much more effectively inside a filter as they water movement promotes oxygen in the water which the bacteria need to thrive.
Without adequate filtration your fish will die or at the very best lead a drastically shortened and painful existence.
Chemical filtration is also available but I wouldn’t waste your money with it for a goldfish tank. Of the chemical filtration options Carbon is the most common but should only be used only after a medication treatment and then removed after a week. If you have plants in the aquarium carbon will suck up valuable nutrients thus starving the plants of food. Active carbon will also counter the effect of fertilising your tank.
Carbon fills up and stops absorbing things after about two weeks and can become very costly to replace, you’re by far better off just using extra biological or mechanical media in its place if your filter has spots for carbon. If you still wish to use it, a much less costly option is SeaChem Purigen. I have no idea what it’s made from but think of it as rechargeable carbon.
Purigen starts off white and you put it into your filter in a stocking, over time it turns black and then you simply recharge it with bleach. The intial cost is quite high but over time it’s a much more cost effective route then using carbon. Be careful to follow Seachem’s recharge instructions carefully as it is possible to ruin Purigen if it’s not done properly.
Right, so now you know the basics of filtration there are four types of filters to choose from, well five if you count corner filters but due to size they are not appropriate for a goldfish tank. For smaller tanks aim for an internal or undergravel filter and for larger tanks a HOB or canister filter.
I’ve written about each of the four main filter types in greater detail, you can follow the links below.
Filter Articles
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