Here A buddy just sent this to me. Check it out.
Water Changes (In Detail)
by Mike Paletta
The topic of water changes for a saltwater aquarium is still a topic that generates a great deal of debate. Part of this is due no doubt to wishful thinking, part due to claims by some hobbyists that they have never done a water change and part due to there being no hard and fast rule as to what is ideal. I still remember vividly the claim of an early trickle filter manufacturer that part of the allure of their filter was that it "Eliminates the need for water changes forever". Unfortunately, experience has taught us that these claims were not only untrue, but were deleterious to our animals as well.
Better filtration methods have allowed for most tanks to no longer need to be completely dismantled in order to be cleaned. However, the daunting task of doing water changes still remains. I would love to tell you that it is no longer necessary to do water changes and I'm sure that many of you have tried or know of someone who has not done a water change for a very long time. Some of these individuals may even have very successful tanks employing this strategy. However, for most of us that overstocks and may overfeed our tanks from time to time this strategy will not work in the long run.
The reason for this is simple: despite all of the breakthroughs in filtration, both chemical and mechanical, no method that I have seen yet removes the harmful substances that accumulate in a closed system. A water change is not just a way to replenish elements that are consumed in a reef tank; this could more easily be done by adding trace elements from a bottle. Rather, a water change is the only way to remove harmful compounds that accumulate over time which filtering does not remove. Even though not all waste products are removed by doing a water change, any that are still in the water become more diluted. This is why when doing a water change it is best to siphon detritus and other noxious material off the bottom where they accumulate during a water change.
There is not a lot of rocket science in doing a water change, but there are some techniques that can make it even more advantageous. First the powerheads should be turned off and the current in the tank reduced. Then, with a bulb baster, any detritus or waste materials can be blown off the live rock and corals. By reducing the current in the tank, the detritus that is present and that is blown from the nooks and crannies will settle to the bottom of the tank. Once the detritus has settled it can then be removed during the siphoning of the bottom.
The reason that it is important to get the detritus out of the tank is that the detritus acts as a nutrient sink from which algal blooms may get their nourishment. Organic phosphate, nitrate, algal spores, etc., are all present in the detritus that accumulates in the spaces in the corals and between the live rocks of every tank. If it is allowed to accumulate to high levels the result will be the rapid growth of algae. The reason for this is that algae are much more efficient at using these end stage waste products than are the corals. As a result when these nutrients accumulate the corals are at a disadvantage in that they are better at utilizing primary waste products, ammonia, fecal pellets, etc. In most areas on the fore reef, the corals are constantly bathed with water low in nutrients. However their bath is so large they are able to take up enough nutrients to sustain themselves. In the lagoon areas more nutrients accumulate and as a result animals from these areas can tolerate higher nutrient levels. This is why corals from these areas are typically good candidates to be the first inhabitants for a new reef hobbyist.
During a water change, the water and detritus should be drawn off and either flushed directly down a drain or drained to buckets lower than the tank so that an equal amount can be replaced. Clean new water should then be poured in to replace it. This water should be mixed so that it matches the old water in terms of temperature, salinity, alkalinity and pH. The match does not have to be precise, but the closer it is to the tank's water the less shock that is produced on the animals.
