From my own experience, there are few factors that actually help to get crystal clear aquarium water which I shall discuss and share here. Bear in mind that the suggestions are based on the assumption that all other external factors are perfect that is, there is no algae bloom, your aquarium is not overstocked and whatever fish supplies that you have added in has been properly rinsed.
The top priority in order to get that extra clear water is that, you must have a stable and established aquarium whereby the nitrate and nitrite is at low level and ammonia is of course at zero percent. During this stage, there is an equilibrium whereby whatever waste generated in the aquarium is efficiently converted to nitrite and then followed by nitrate by the bacteria that populates your aquarium. That is why it is very common to see all newly-setup aquariums will have cloudy water at the beginning stage.
Second, the type of filter is also another consideration. Aquarium filter not only plays important role to clear out the small debris by means of mechanical filtration but the filter media especially nylon wool is a perfect spot to establish your colony of beneficial bacteria. The difference is very obvious because you can see a large variation in terms of water clarity between an aquarium that use the right type of filter including the filter media and another aquarium that uses an undersized, inefficient, cheap filter. For the best clear water result, I usually recommend using either undergravel or overhead power filter with nylon wool as the media.
Whether you have live aquarium plants is also another factor that will enhance water quality. There are many benefits attached to it because not only does presence of plants help to enhance achieve crystal clear water, but they also help to establish the equilibrium needed as mentioned before in the Nitrogen Cycle. In fact, whatever waste present in the water is actually nutrients, to be utilized by the aquarium plants, and thus this helps towards getting the best water clarity.
Sometimes there are certain aquarium water clarifier solution which can be bought at aquarium stores and mix to the water to achieve crystal clear appearance. I do not suggest using this type of clarifier aid because basically what the chemical does is to bind together the small debris and fine particles to form larger molecules which are then easier to be filtered and captured when passing through the filter media. There’s a risk however, because basically there’s a possibility that the binding agent with the particles may collect and stuck at aquarium corners and tight spaces causing a whole lump to be collected there. Another potential risk to consider is the harm and adverse effect to the health of your fish if overdosing of the chemical occurs.
Having crystal clear aquarium water is very important not only does it enhance the beauty of your aquarium and lets you see and enjoy the fish much better but it is also projects your skill towards quality maintenance and your overall way of managing the small ecosystem. Other benefits also is that with cleaner water, expect the health of your pets to improve considerably.
Related topics: How to treat and condition tapwater for aquarium use and performing pH tests