Do You Need a Filter for Your Fish Tank

By Eddie Waithaka @aquariawise

What Happens If You Don't Put A Filter in A Fish Tank

As a newbie in the aquarium fish keeping hobby, I was a little intimidated by the somewhat steep learning curve. Bombarded by the endless fish and plants options and equally perplexed by the necessary and not so necessary aquarium equipment.

One question I struggled with and still pops up in my radar is “Do I need a filter for my fish tank?”

Quick answer: Almost certainly yes! This I’ve learned with time

Of- course, assuming we are talking about freshwater tanks, since most saltwater tanks are actually filterless but with protein skimmers and live rocks.

In theory, the only feasible freshwater filterless setup would be a high-end, densely planted tank with enough lighting and often CO2 addition. Plus understocked with fish, if any.

Hence, in most cases, you will need a filter for any or all three aquarium filtrations types: mechanical, biological and chemical.

Typically, you’ll either use a sponge, hang-on-back, under gravel or canister filter. Very likely one with superior biological filtration capabilities.

That said, let’s dig a little further just so I explain why a filter is so imperative on almost all fish tank setups.

We’ll look at:

What Does a Filter Do in a Fish Tank?

The function of a filter in a tank is double: water movement and to remove both soluble and insoluble dirt from the water.

The process of cleaning the aquarium water using a filter is called the nitrogen cycle, particularly when referring to the biological filtration process.

There is a slight chance your tank could work without a filter but you will need something else to accomplish the filter functions.

Water movement can be easily achieved by adding an air pump.

The nitrogen cycle is, however, trickier because you will need a considerably thick substrate and plenty of live plants.

To best appreciate the need or lack thereof a fish tank filter, you’d have to conceptualize the source of dirt in your fish tank.

Ordinarily, rotting leftover food, fish waste, and decomposing plants are the major dirt factories in any setup. And for this, you need a mechanical filter to trap any floating debris.

Also called physical or particulate filtration, the mechanical process is provided by pushing water through some form of filter media that act as a strainer. It generally catches floating particles using a sponge, filter floss, special filter pad or aquarium gravel media.

However, the dirt ruckus doesn’t end there, because apart from the particulate dirt, fish waste and decaying organic matter give out toxic chemicals which have to be filtered out too.

If you fail to filter out these toxins you will very easily and quickly kill your fish.

Here, a biological filter that involves bacteria and other microorganisms convert your fish waste toxins into less toxic substances.

Since fish mostly produce ammonia in waste, the biological filter will normally convert this toxic substance into nitrites then nitrates which are relatively harmless to the fish.

Though long exposure of your fish to the nitrates could cause gradual kidney, liver, eye problems and encourage algae growth in your tank.

Notably, a biological filter is the barest minimum in a fish tank even remotely likely to support living inhabitants.

Finally, chemical filters generally deal with any other toxins that might be present in your aquarium. They typically use carbon or chemical resins to extract these elements.

Despite that, here are a few more questions you’re probably asking yourself in regard to fish tank filters.

Does a Filter Oxygenate a Fish Tank?

Just like humans, fish need air to live, which means your aquarium needs to be properly aerated, especially if yours are don’t have labyrinth organs hence incapable of taking air from the water surface.

So, is it really possible to oxygenate your aquarium with a filter?

Technically YES!

Conventionally, most people will use air pumps in their aquariums, but this means you’ll need more space to hold both equipments. So, if you have a small fish tank, it OK to use your filter as the prime aeration kit.

Opt for a powerful filter which is more effective at adding oxygen to the water that flows through it. By design, the higher the filter’s flow rate and the pressure of the water coming out of it, the better aerated your aquarium water will be.

For the most part, a simple Hang-On-Back filter will adequately aerate most fish tanks. Regular HOB filters have an output that drops water into the surface of the tank which provides adequate surface agitation.

Additionally, this filter circulates the water in your tank which is desirable since the bottom content will cyclically move to the top. Atop the aquarium, the water is in contact with the atmosphere, hence tend to have a better oxygen concentration.

An alternative would be to buy a filter and air pump combo. Especially if you have a big tank and your filter aeration capacity is not adequate.

Assuming you get a reliable and well-designed combo, there will be no reason to push your filter to work as the primary means of oxygenation.

Plus you don’t have to go out and find two separate items that need to work together perfectly.

Do You Have to Clean The Tank if you Have a Filter?

I guess the most important thing to realize is an aquarium filter does purify your water but certainly doesn’t clean your fish tank.

When cleaning your aquarium, apart from the weekly water change, there is a whole lot more involved. Well, maybe not too much but you At least need to:

  1. Vacuum the gravel and remove any algae and uneaten food stuck down there.
  2. Wipe the aquarium glass or acrylic surface to remove grime and any algae. Plus check the filter and clean any blockages or debris built up in the filter media or intake.

That said, even with a filter, I’d recommend you clean your fish tank at least once every one or two weeks.

And if your aquarium is heavily stocked or you have messy fish in there, the cleaning sessions will have to be more frequent.

In short, a filter will keep the aquarium water clean and free of toxins, sometimes even help oxygenate your water. But cleaning the substrate, glass or acrylic surfaces, plants and decorations like rocks and driftwood will entirely remain your responsibility.

What Happens if You Don’t Have a Filter for Your Fish Tank?

If you have a plant only aquarium, not having a filter is not entirely unheard of, sometimes even properly planted tanks with a few fish might function without a filter.

If you’ve asked around, I’m sure one or two hobbyists have told you it will depend. Which is not entirely misleading because there are fish which do OK with or without a filter in their tanks.

Which we will look at shortly!

Also, with simple small fish tanks, you can remove the fish, clean the tank, replace the water and return the fish. However, this is not only stressful for you since you’ll have to repeat this process every week. But also stressful to the fish because you keep changing its environment.

So by and large, there is no denying filters make your life easier and are most of the time the difference between your fish living or dying. So if you have a basic fish tank, anything that doesn’t qualify as a fishbowl, get a filter. Unless you want an aquarium full of dead fish.

Can Fish Survive Without a Filter? (Here are a Couple That Can)

Generally,if you are happy keeping very few small fish in a tank that’s heavily stocked with living plants, there are a few species that might survive.

The plants must be healthy and robustly growing and dense. Also, for this to work, the water must be circulated constantly. Need not to be fast, but it must be moving. Plus adding air stones should help.

You should also be willing to do LARGE water changes two or three times a week. Which will use up a huge amount of water and if you stock a fish too many, you risk losing them should you forget to change the water even once.

In a small to an average fish tank, without a filter, you can only keep around 5-6 small fish at most and you should change the water regularly.

However, remember that different fish produce varying kinds of waste, therefore you’ll need to adjust the amount of filtration accordingly.

And make the perfect fish choice for your filterless fishtank.

For instance, goldfish are small but produce a lot of waste hence not the best candidate for a filterless tank.

Sadly, I’ve only tried guppies and betta successfully in a considerably small filterless tank.

But from my research, I’ve found a few other species that may survive without a filter.

My Two Cents

Different species of fish have varying water needs, so not all fish kept by hobbyist need filters. Bettas and goldfish are two hardy species that will survive long enough without a filter.

However, if you want to give your fish a longer happier life, it’s imperative to have a filter for your tank. This will protect them not only from visible dirt elements but also toxic chemicals that may accumulate in the water.

If Not, considering many aquarists are moving towards filterless tanks, at least make sure your tank is densely planted and properly circulated.

Preferably, with an air pump and also aerated with an airstone also called an aquarium bubbler.

Then create a strict water change schedule at least once or twice a week depending on your fish species.

To stop dirt from accumulating in your fish tank, avoid overfeeding your fish and remove any uneaten food every so often. Frequently clean your substrate by vacuuming the gravel and pebbles.

Granted, if you have a generous size aquarium, it only makes perfect sense to have a filter.

The only reason you should not have a filter in a big tank is when it’s a planted aquarium, and even those, still need filters at times.

Enjoy your fish tank.

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