About RO, UV, and Carbon
Reverse Osmosis (RO)
A reverse osmosis unit provides a supply of purified water.
Tap water can have varying characteristics, particularly as to its mineral content. Using an RO unit can rectify these problems.
The tap water is forced through a membrane, the pores of which let water through, but retains the larger molecules of dissolved substances. As the membrane is semi permeable, the water cannot take the reverse path and return to the other side of the membrane. This allows the purified water to exit "downstream" whilst the dirty water exits "upstream".
Most RO units are equipped with pre-filters to retain molecules such as chlorine which could damage the membrane.
The efficiency of the RO unit is determind by the regular cleaning of the membrane. It is impotant to follow the manufacturers instructions at all times.
In terms of quantity, the efficiency of an RO unit is around 25%, which means that of the water put through the unit, one quarter of the water passed through the membrane is passed downstream, with the remaining three quarters (dirty water) being discharged upstream.
Membrane - a film which allows the passage of molecules smaller than the size of its pores.
Semi Permeable Membrane - One which can only be passed through one way.
Polymer - Chemical compound formed of long chains of molecules
Ultraviolet Sterilization (UV)
UV sterilizers are used to kill viruses, parasites and unwanted bacteria. Few freshwater systems use UV, but most Marines systems are operated with a UV unit installed.
The way a UV sterilizer works is very simple. The water to be purified passes past the UV lamp which is contained in the UV unit. The UV light penetrates the water (which is passing through the unit), this breaks down the cells of the living organisms which are in the water. This effect allows aquariums and ponds with green water problems to have clear water, and aquariums where parasites are to be prevented, are run clear of parasitic problems.
In an aquarium, UV sterilizers are used in conjunction with an external filter, either a cannister filter or a trickle filter. Most UV units are connected on a "branch" with reduced flow from the filter, rather than a main circulation hose. This allows the water to pass through the unit more slowly, therefore increasing the "contact time".
The basic principle of activated carbon is the removal of undesirable molecules by trapping them in the pores and outer surfaces of the carbon. Activated carbon is made from charcoal which is obtained from the burning of materials such as wood, coal, peat etc. In the charcoal state, this contains phosphorus, sulphur and heavy metals which are undesirable in an aquarium.
Activation of the charcoal eliminates all these elements except the carbon, which increases its porus nature.
Carbon in the aquarium "cleans" the water, making for clearer viewing, it removes low levels of nitrates, phosphates and metals. It also reduces the effect of medicines in the aquarium, and MUST be removed before treatment commences.