Posted by @Chris_Lewis · 2h ago
I see wildly different advice on this, so here's how I actually think about it after years in the hobby.
There's no universal number ... it depends on your stocking level, tank size, and how heavily you feed. A lightly stocked, well-planted tank can coast on a 25% change every two weeks; a packed tank with big messy eaters might want 30–50% weekly.
Let your test kit decide, not a calendar. The number that matters most is nitrate. Pick a ceiling (a lot of people use ~20–40 ppm) and change enough water, often enough, to keep nitrate below it. If nitrate climbs past your line before your next scheduled change, you're either changing too little or too infrequently.
A few things that trip people up:
- Always dechlorinate new tap water, and match the temperature so you don't shock the fish.
- Don't deep-clean everything at once — scrubbing the tank and rinsing filter media in the same day can knock back your beneficial bacteria.
- Consistency beats heroics. Small regular changes are far better than a giant rescue change once a month.
What's your routine , tank size, stocking, and how often you change? Curious how much variation there is here.