Water changes for a reef aquariums in SEQ.

Why do water changes for reef aquariums and why do we dose?

With adequate amounts of algae and a properly designed bio system, which includes the use of algae looking after your waters impurities, then you may never need to do a water change?
You see algae used correctly will take out the entire nutrient content, organic and inorganic and toxins and general water-soluble rubbish from your reef aquariums waters! The drawbacks to the use of algae for these purposes is that they need most of what your corals need for their own cellular reproduction!
Substances like magnesium and calcium carbonate to name just two, the algae you are using for importing onto exporting will extract/import then you throw the algae away . take these out at a rate much quicker then the corals algae can achieve, from these facts it becomes obvious that giving your corals such affective protection will adversely affect your corals by reducing valuable elements that you need to dose with!
If you use for importing, such as a small amount of algae supported by bio cubes titanium and standard cubes with a little activated carbon and a small but affective skimmer, all these combined will take away the need for water changes completely as well, but you have gained only a little towards reducing the limiting of substances required by corals to grow.
Water changes will put back some of what is required for coral growth, but only in small amounts!

First up, the benefit of water changes by reducing these.
1.From all that was alive in your water, there are inorganics produced from the waste/dead tissue products that are present near to and at the end of the nitrogen cycle.
During oxidation, of which occurs at either side of the nitrite part of the nitrogen cycle, what is left is not just nitrate but also orthophosphate, phosphorus, metals and toxins that exist and build with in tissue of all life, including us!  
These have to be taken out of the water or converted via photosynthesis to keep corals symbiotic algae from being burdened turning its algae rogue by dropping its valued pigments allowing the onset of xanthophyll pigment fucoxanthin to the corals disadvantage and else where in the aquarium increase the appearance of cyano and unwanted algae types that feed on what oxidation processes leave behind.
2.The next is the stain “colour in your waters that defuses lighting” that comes from all that is dead or from what has been excreted.
3. The last and rarely thought of is that most aquarium life, especially corals, which includes anemones, zoas, sps lps, etc,etc, these are all corals, then you have acidians,sponges, the list is enormous, of what excretes “toxins” while alive or once dead and being broken down by bacteria!!!!

These are what kills most marine aquarium fish and sickens your corals leading to a progressive decline in health, onto death!
Your fish drink constantly to off set osmotic absorption of surrounding saltwater, that means salt is trying to get in at all times just like us if we are in salt water for to long making us dehydrated, so your fish drink a lot of the water that they are swimming in.
They expel the salt via mainly two organs just like our RO filters and apply the left over freshwater to their pores where the salt is trying to enter!
What’s in the water that you can not see and many you can not test for, is getting into your fish constantly and then into their organs and blood stream!
So you either do water changes or apply measures that will take all of these out of your waters.
There are man made ways and you can combine ways that land plants and phytoplankton have been carrying out to keep all that has been and is still alive on this planet for many millions of years and before them, still going strong today from billions of years back, are cyanobacteria.
From all this it becomes clear that wether you use water changes, algae or purchased products, you most certainly need to dose/return substances to the water that your corals require for its own structural demands.
Like a city, there will be more people/polyps made, but with out these as only part examples, concrete and steel/calcium and magnesium build the cities for us and the corals polyps that both of us need in order to exist!