Tank Setup
Water change
Gallons removed, conditioner mL, and tap-versus-tank temperature gap.
Results
Remove / replace
10.0gal
Left in tank
30.0gal
Dechlorinator
10.0mL
Temp gap
6.0°F
Adjust the new water by about 6.0°F before adding it — a sudden swing can stress fish.
Dose is based on new water volume. Always follow your product label.
How to use this
- Enter tank volume and the percent you plan to change (25% weekly is a solid default for stocked tanks).
- Set your conditioner dose rate from the bottle (often ~1 mL per gallon of new water — check the label).
- Compare tank vs tap temperature; match within ~2°F before adding water.
- Export the CSV if you track maintenance logs.
Math
- Gallons removed = tank × (change% / 100)
- Dechlorinator mL = gallons removed × dose rate
- Temp gap = |tank °F − tap °F|
25% weekly at 1 mL per gallon of new water
Dose the water you add, not the whole tank. If the bottle is 1 tsp per 10 gallons, convert once and stick to it — teaspoons vary.
| Tank | Remove / add | Conditioner |
|---|---|---|
| 10 gallon | 2.5 gal | 2.5 mL |
| 20 long | 5 gal | 5 mL |
| 29 gallon | 7.3 gal | 7.3 mL |
| 40 breeder | 10 gal | 10 mL |
| 55 gallon | 13.8 gal | 13.8 mL |
Worth knowing
- Vacuum detritus while water is lowered — do not deep-clean all filter media the same day.
- Planted EI tanks often use larger (40–50%) weekly changes by design.
- If tap has chloramine, use a conditioner that explicitly detoxifies it.
Usual mistakes
- Dosing conditioner for the whole tank when only replacing a fraction.
- Pouring ice-cold tap onto tropical fish.
- Changing too little water on an overstocked goldfish tank and wondering why nitrates climb.
See also: Tank Volume · Fertilizer · Stocking