PRINCIPLES OF FILTRATION

The whole concept of filtration is to clean the water of impurities. Any pet will leave waste which can be physically removed, but in the confines of an aquarium where waste is dissolved in water there has to be a different procedure. In addition there may be waste or other contaminants in the water prior to its use.
Let us now consider various forms of waste or undesirable elements, this consideration falls into two neat areas.
1) Elements already in the water.
2] Waste produced by urine and faeces and from the breakdown of uneaten foods or decomposing plant life.

ELEMENTS ALREADY IN THE WATER

Water types range from fresh to esturine and brackish to sea-water.
I live in the North of Scotland where we have some of the purest water in Europe but a recent analysis revealed the following naturally occuring constituents present.
Sulphate; Magnesium; Sodium; Potassium; Nitrate; Nitrite; Ammonium; Aluminium; Iron; Manganese; Copper; Zinc; Phjosphorus; Fluoride; Silver; Arsenic; Cadium; Cyanide; Chromium; Mercury; Nickel; Lead; Antimony; Selenium; Chloride; Calcium; Boron; Barium; and many others. This is not all surprising as water is the universal solvent which explains how these constituents are present. Fortunately they are in the main small and insignificant in quantity. In addition there is the contamination produced by man.
Generally speaking the water that comes out of your tap is by and large quite suitable except where chlorine, a disinfectant, is added. This substance leads us to the first instance of cleaning water for fish. Fill a bucket with water, leave it standing for at least 24 hours and the chlorine will have dissipated into the air. The process can be hastened by vigorous agitation or boiling. For greater refinement we should consider other processes.

REVERSE OSMOSIS
Here water is forced through micro filters and emerges about 98% pure or so the makers say. The disadvantage for me being that the unit needs must be plumbed in and a high percentage of the input must be discarded and as I am concious of the environment this appliance is not for me. Having said that they are very effective is removing the majority of contaminants.

ION EXCHANGE RESIN
A by-product of space research the concept of using resins to clean water now forms the greater part of the commercial filter market. Many models of this type of filter can be purchased but any reasonable DIY person can make their own. The advantages are I believe considerable, apart from cost not the least of which is purchasing replacement resins. Making your own can ensure that you have the correct output of water for your set-up, the design can be such that it fits into whatever space you want and the resins can be re-activated. The biggest advantage being that all water input is used therefor no waste.
I do have a DIY diagram available for those who wish it.

POST TANK FILTRATION
Using a pump of some description we take water from the aquarium, pass it through a filter and send it back into the tank. A note of caution here is that when calculating medication for a tank do take account of the quantity of water contained within the filters, which by the way should be removed if using medication.

MECHANICAL FILRATION - For Suspended Matter
This should form the first section or part of the filter system and as the water passes through, solid particles of waste and uneaten food are passed through media acting as a barrier or filter. The finer the material the more efficient the system. Commercial sponges, floss and such can be bought but I have used old net curtains, ladies tights [minus the occupants] and similar. Other materials are sand, gravel, diatomic earth etc. The main consideration being that the material used is inert and does not leach toxic substances, is clean and free from dust and is changed or cleaned frequently.
NEVER wash the material in fresh water as the beneficial bacteria colonising it can be destroyed. use spent water from the tank, as in routine water changing, to clean filters.
This will remove many suspended particles but not those in solution.

CHEMICAL FILTRATION - For Elements in Solution
Suspended particles combine with each other to make aggregates which in turn amalgamate to become detritus , which is the mulm seen in many tanks.
The main item in solution is protenious matter and for this we can use a protein skimmer , which concept originated in the sewage disposal industry. You can observe the action for yourself at any sewage outlet running into the ocean where you will observe a scum of soapy bubbles which hold in suspension many pollutants that are protein in composition. This then is the basis of our skimmer which removes the scum. Regarded by many marine life enthusiasts as essential equipment.
The resins discussed earleir can also play a role here.

BACTERIAL FILTRATION - The Natural Method
This is described in many publications as the Nitrogen Cycle . and will not be gone into detail here. Suffice to say that essentially two groups of naturally occurring bacteria are involved and are called Hetrotrophic meaning they take their sustenance from from waste products such as proteins, the second are Autotrophic , meaning they covert chemicals into food.
These bacteria colonise filter media and break down many undesirable elements into elatively non-toxic substances.
Whatever filtration is used there is really no substitue for water changing. At least 10% of the tank water should be changed weekly, the result will end with healthy stock and a tank that is a pleasure to look at.

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