Join Date: Oct 2007
Location: Ontario, Canada
For a low-tech tank, you do not need to do too many water changes for a number of reasons.
Plants adjust to CO2 levels in the water. When tank water is low in CO2, such as in low-tech settings, plants produce a CO2-fixing enzyme called rubisco. However, when you do WCs w/ fresh tapwater, which is high in CO2, you are tricking the plants into thinking they are in a high co2 environment. They stop producing rubisco, but then co2 decreases shortly after. Same thing with algae, except they respond much faster to co2 changes, so essentially you will be inducing algae growth.
Frequent water changes simply resets the nutrient level to whatever is present in tapwater. If you have more nutrients in tank than tapwater, it will be removed, vice versa. It's an easy way to control nutrient levels.