Water changes are one of the most reliable ways to keep guppies thriving. They remove dissolved waste, dilute nitrates, and stabilise conditions. But many keepers get stuck on a “rule” like 20% weekly without considering how different tanks behave. The right routine depends on stocking, feeding, and how quickly nitrates rise in your particular system. When you choose the right percent and frequency, fish health becomes more predictable.
What water changes actually do
- remove dissolved organics and excess nutrients
- control nitrate trend over time
- reduce the risk of sudden crashes from accumulating waste
How to choose a routine
- Watch nitrate trend: if nitrates rise quickly, increase change size or frequency.
- Consider stocking: more fish = more waste, even with good filtration.
- Consider feeding: heavy feeding grows fish but also grows waste.
Small frequent vs bigger weekly changes
Both can work. Small frequent changes keep conditions very steady and can be great for breeding and fry growth. Bigger weekly changes are simpler and still effective when done consistently.
Safety tips
- always dechlorinate new water
- match temperature as closely as practical
- avoid huge changes only when your parameters swing wildly (stability first)
There’s no perfect percentage that fits every tank. The best routine is the one you can do consistently that keeps water stable and nitrates controlled. Guppies respond to steadiness more than anything.
