Five ways for you to achieve crystal-clear aquarium water


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Crystal-clear water isn’t a target that we all strive for with the rise of the Biotope aquarium and blackwater tanks. However, it’s still what the majority of fishkeepers aim for so, what methods help to achieve that goal?

Image above: Tank by Darren Dalton of Seahorse Aquariums, Dublin.

Let’s start with the basics. Is your filtration and circulation up to scratch? Many methods of improving water clarity rely on your filter system – be that different media within the filter or equipment used in conjunction with your filter. This makes external filters and sump tanks far more suitable than their internal counterparts.

This is due to their substantial capacity, ease of adding alternative media and because the pipework allows other equipment to be used in-line, either before or after the filter or sump itself.

Circulation isn’t necessarily all down to the filter, but it always has a considerable part to play in moving water around the aquarium. A turnover of 5-10 times an hour is needed for effective filtration and clean water. Still, the force of circulation can be wildly different when dispersing the flow with a long spray bar compared to a single nozzle outlet.

Pay attention to the circulation when positioning and setting your filter up. A helpful way of testing your circulation is to release a pinch of flake food in front of the filter outlet and see how it moves (this can also be done with a coloured medication or treatment when it is called for).

If a particular area of the tank is getting little in the way of water movement, either try repositioning your filter, or filter inlet/outlet, or use an additional circulation pump to deal with it. A still corner can collect settled waste which, when disturbed by fish, will cloud the water column.

If you find you don’t have enough capacity in your external filter, then you can add an in-line pre-filter. Pre-filters simply add more space for media. They tend to be aimed at mechanical filtration containing several layers of sponge – going from course to fine sponge in stages.

For some, this allows more capacity for bio-media in the external filter for big fish or heavily stocked aquaria. For others, it will enable more space for mechanical filtration, such as graded filter flosses and chemical media - to reach the goal of super clear water.

Very fine mechanical filter material, known as filter floss, will trap the finest particles of solid waste before the water returns to the aquarium. The downside – it clogs far quicker than fine sponge media, so filter maintenance may be needed more regularly to avoid the flow reducing.

To stretch-out the maintenance periods, it’s important to place floss after any course and fine sponges in the filter, but before bio-media and any chemical media, you might employ.

Some manufacturers produce floss media of different grades, such as the three types of Mega Media by Aquarium Systems, being able to extend maintenance periods further.

Using Chemical media is the next stage. Activated carbon is the most commonly used chemical media, but it’s often a little misunderstood. Many people will incorrectly, habitually use carbon to keep water quality in check.

Essentially, carbon will polish the clarity of aquarium water and remove odours. Tannins and phenols get removed efficiently – taking the brown or yellowing colour, and any aroma, away - leaving it sparkling. For a further understanding see:

Some chemical media do more for water clarity. Highly porous scavenging resins, like Seachem Purigen, can adsorb both soluble and insoluble impurities efficiently.

Other chemical media concentrate on removing waste products like nitrate, phosphate and silicates, each of which encourages algae growth. Algae rarely cause a problem with water clarity, but single-celled algae (green water) can add a haze to an aquarium or turn the water pea green, in extreme cases. Also, there is little point in striving for crystal-clear water when algae on the glass obscures your view.

Ultra Violet (U.V) light is a type of radiation used for clarifying water and killing pathogens. U.V clarifiers have limited contact with water; they are efficient at killing water-borne algae and are an aid for good clarity. 

U.V sterilizers employ more powerful U.V bulbs, have closer water contact and often require a slower flow rate. Hence, radiation exposure is higher. Sterilizers are strong enough to kill a whole array of microorganisms, including pathogenic parasites and bacteria, as well as encouraging extreme clarity.

With all things equal, you really notice the extra clarity of an aquarium with U.V filtration. Just remember, a lot of medications are de-natured by U.V, so it is likely that you will need to turn it off if ever you need to medicate.

U.V filters are available as separate, submersible units, as exterior units which are rigged-up to the pipework of an external filter or sump, and are built-in to some external filters. So, there’s a U.V to suit all set-ups.