Posted by Chris Lewis ·
If you've gotten a different answer every time you asked, here's why: the right schedule depends on where your tank is in its cycle. Once you know that, the answer is simple.
If the tank is still cycling (fish-in)
A new tank doesn't have enough good bacteria yet to process fish waste, so ammonia builds up. Until the cycle finishes:
- Test ammonia and nitrite every day or two.
- Do a water change whenever ammonia plus nitrite reaches about 0.5 ppm. In a 5 gallon with one betta, that might be every two to four days.
- Change about 30-50%, with dechlorinated water at the same temperature.
- Don't clean the filter, and never rinse it in tap water. That's where the good bacteria live.
Three weeks is usually not enough. Most fish-in cycles take four to eight weeks. It's done when you've had zero ammonia and zero nitrite for a week or more, with nitrate showing up.
Once the tank is cycled
- One water change a week, 25-30%, is a solid routine for a small betta tank.
- Vacuum the gravel where waste collects, part of the tank at a time.
- Rinse the filter sponge in removed tank water only when flow slows down, roughly monthly.
- Test weekly for the first couple of months, then whenever something looks off.
Not sure where you are? Put your test results into our Water Check. It tells you whether you're cycled, mid-cycle, or have a spike, and exactly what to do next.
Background reading: nitrogen cycle, ammonia spike, betta care.