Aquarium Evaporation Rate Calculator
Created by: Ethan Brooks
Last updated:
Calculate daily water evaporation based on tank surface area, water temperature, room humidity, and tank type. Plan auto top-off (ATO) reservoir sizing and understand how evaporation affects salinity in marine tanks.
Aquarium Evaporation Rate Calculator
AquariumCalculate daily water loss and plan auto top-off needs based on tank conditions
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What is an Aquarium Evaporation Rate Calculator?
An Aquarium Evaporation Rate Calculator estimates daily water loss based on tank surface area, water temperature, room conditions, and tank type. Understanding evaporation is crucial for maintaining stable water parameters, especially salinity in marine aquariums.
This calculator helps you plan top-off water needs, size auto top-off reservoirs, and understand how environmental factors affect your tank. Proper evaporation management prevents salinity swings that stress corals and fish.
Evaporation Rate Formulas
Basic Evaporation Rate:
Evaporation (gal/day) = Surface Area (sq ft) × Evaporation Factor × Temperature Factor × Humidity Factor
Surface Area:
Surface Area = Length × Width (accounting for water line, not tank dimensions)
Typical Rates by Tank Type:
• Covered freshwater: 0.5-1% volume/day
• Open freshwater: 1-1.5% volume/day
• Covered marine: 1-1.5% volume/day
• Open reef with sump: 2-4% volume/day
Impact on Salinity
Freshwater Evaporation: Only pure water evaporates. Minerals, including salt in marine tanks, remain behind. This concentrates dissolved substances and raises salinity.
Salinity Calculation: If 5% of water evaporates from a 1.025 SG tank, salinity rises to approximately 1.026 SG. Without correction, continued evaporation can quickly reach dangerous levels (1.028+).
Top-Off Rule: Always replace evaporated water with freshwater (RO/DI for marine tanks). Adding saltwater would compound the salinity increase.
Frequently Asked Questions
How much water does an aquarium lose to evaporation?
Typical aquariums lose 1-2% of their volume per day to evaporation. A 50-gallon tank might lose 0.5-1 gallon daily. Factors include surface area, water temperature, room humidity, and air circulation. Reef tanks with sumps and skimmers often experience higher evaporation rates.
Why does evaporation increase salinity in saltwater tanks?
When water evaporates, only pure H2O leaves - salt and minerals stay behind. This concentrates the remaining salt, raising salinity. A tank losing 1 gallon daily could see salinity rise from 1.025 to 1.028 in just a few days without top-offs. Always use freshwater (RO/DI) for top-offs, not saltwater.
What factors affect aquarium evaporation rate?
Key factors include: surface area (larger = more evaporation), water temperature (warmer = faster), room humidity (drier = faster), air movement from fans or AC, open vs. covered tank, and equipment like protein skimmers. Reef tanks with sumps typically evaporate 2-3x faster than covered freshwater tanks.
Should I use a lid to reduce evaporation?
Lids reduce evaporation by 50-70% and prevent fish jumping. However, lids can reduce gas exchange and light penetration. Many hobbyists use partial covers or egg crate. Reef tanks often run open for better gas exchange, accepting higher evaporation rates.
What is an auto top-off (ATO) system?
An ATO automatically replaces evaporated water using sensors and a pump. It maintains stable water level and salinity. Essential for reef tanks and helpful for any aquarium. Basic ATOs cost $50-100, while advanced units with redundant sensors cost $150-300.
Can I use tap water for top-offs?
For freshwater tanks, dechlorinated tap water is acceptable but adds minerals over time. For saltwater tanks, use RO/DI (reverse osmosis/deionized) water only. Tap water top-offs in marine tanks cause problematic mineral and nutrient accumulation.
How does room humidity affect evaporation?
Lower humidity = faster evaporation. A tank in 30% humidity evaporates roughly 2x faster than at 60% humidity. Winter heating dries indoor air, increasing evaporation. Summer AC also reduces humidity. Monitor room humidity during seasonal changes.
Why does my reef tank evaporate so fast?
Reef tanks have multiple evaporation sources: main tank surface, sump surface, protein skimmer operation, and higher water temperatures (78-80°F). Combined with typically being uncovered for gas exchange, reef tanks can lose 2-5% of volume daily.
Sources and References
- Reef Builders, "Understanding Evaporation in Reef Tanks", 2024
- BRS TV, "Auto Top-Off Systems Guide", Bulk Reef Supply, 2024
- Marine Depot, "Salinity Management Best Practices", 2024