Originally Posted by lovemygoldy
Don't remember where I heard it, but I believe someone said that as long as you do water changes that add up to 100% a month you should be fine. Like a 50% twice a month, or a 25% once a week. I usually do like a 25-50 every 1-2 weeks, depending on how the water looks and what the levels are.
It's worth bearing in mind that some people do not like doing water changes, and knowledgeable staff in good stores and other aquarists know this, and may sometimes suggest less-than-optimum schedules in the hope that at least some water will get changed on a somewhat regular basis. I obviously do not subscribe to this school of thought. If one is going to keep fish (just like any animal pet) one has to recognize that the responsibility to look after it is part of the experience. And with fish, that means regular water changes.
Doing 50% every other week is better than nothing, but doing 25% each week is much better. In nature, fish live in water that is either constantly moving past them (streams, rivers, creeks) or in a lake that has considerably more volume that will be affected by the fish population. In both cases, the water around them is not static but changing, which means the toxins the fish expel (ammonia through respiration, excrement, urine) is not staying where the fish is forced to live in it, but moving away. At the same time, the water is bringing minerals and oxygen to the fish, and there is no danger of the fish using all the available minerals or oxygen because of the water movement. In a lake the thermal currents constantly keep the water in motion to avoid stratification. The African rift lakes are a good illustration. They are so deep that the lower water strata never mixes with the upper surface water. It is no surprise therefore that the cichlids do not live in the lower levels. They would in fact asphyxiate if they moved into those regions.
I mentioned my earlier post before, but as it is germaine to this particular issue, I'm going to repeat some of it. As was the thrust of that thread, the issue is not how the water looks or what the nitrate reading might be that determines the need for a water change; its an absolute necessity (for the health of the fish) regardless of how good the water quality may be.
The aim is to maintain consistent water quality permanently. This is not as impossible as some may think. There are fluctuations that occur naturally, in nature and in our aquarium. Fish have evolved to adapt to these minor fluctuations. This involves temperature and pH (there are diurnal fluctuations both in nature and in an aquarium), hardness, and dissolved organics in the water. Fish are very closely tied to their environment. As an example, fish take in water through their cells by osmosis. The fish must adjust its internal pH to equal that of the water passing into its cells. In an excellent article on "Fish Growth vs. Tank Size" in the December 2006 issue of TFH, Laura Muha notes that "Both salinity and pH affects a fish's growth rate because they affect how hard a fish's body must work to maintain its physiological equilibrium--that is, the complex chain of internal chemical reactions that keep the pH of its blood steady, its tissues fed, and its immune system functioning. When pH and/or salinity stray outside the ideal range for any given species, the fishes' bodies must work harder and use more energy to maintain this equilibrium." We all know how stress affects humans, and it is now known that this occurs with fish as well. Having fluctuating water conditions means the fish is constantly having to adjust its metabolism, and this stresses the fish and can lead to poor health, disease, and even death if not corrected. The point of regular water changes is establishing an equilibrium in the tank and therefore in the fish, resulting in healthier and happier fsh. Changing 25-40% of the water every week is maintaining such a balance, because it ensures that the pH will remain relative constant, along with the levels of minerals in the water, and the nitrate level.
Many who keep discus change this much water every day. It would obviously be good for all our fish if we could manage a partial water change every day, but I know that I would have difficulty achieving this.