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Calculate aquarium water volume in gallons and liters for rectangular, bow-front, cylinder, and corner tanks including substrate and displacement.
Calculate CO2 injection rate for planted aquariums from tank volume, target pH, KH carbonate hardness, and bubble rate for stable dissolved CO2.
Calculate aquarium heater wattage from tank volume, room temperature, target water temperature, and desired heat-up time for stable tropical temps.
Classify species as peaceful, semi-aggressive, or aggressive. Peaceful community fish (tetras, rasboras, corydoras) cannot coexist with fin nippers or territorial cichlids.
Compatibility = Temperament tier match ± 1 levelCompare pH, temperature, and hardness ranges. Species with overlapping ranges thrive; mismatched parameters stress fish even if temperaments align.
Compatible if: pH ranges overlap AND temp ranges overlap AND hardness ranges overlapApply the one-inch-per-gallon guideline as a starting point, then adjust for bioload, activity level, and territorial footprint. Cichlids and plecos need more space per inch.
Minimum tank = max(species A min tank, species B min tank)Updated: July 2026
Neon tetras, ember tetras, and pygmy corydoras share peaceful temperament, 72–78°F, and pH 6.0–7.5. All fit a 20-gallon with proper school sizes (6+ tetras, 4+ corys).
Tiger barbs (semi-aggressive, fin nippers) with guppies (peaceful, long fins) are incompatible — barbs will harass guppies. Barbs work with fast-moving danios or other barbs.
Mbuna cichlids need pH 7.8–8.6 and 78°F — incompatible with soft-water tetras at pH 6.5. Stock only with other Rift Lake cichlids in 55+ gallon tanks with rock territories.
Discus (pH 6.0–7.0, 82–86°F) and goldfish (pH 7.0–8.0, 65–72°F) cannot coexist despite both being 'peaceful.' Parameter overlap is mandatory.
A single tetra is stressed and vulnerable. Always buy minimum school sizes: 6 for small tetras, 4 for corydoras, 8 for rasboras. Budget for the full school upfront.
Adding incompatible fish leads to aggression, stress, and losses. This calculator checks species compatibility based on temperament, minimum tank size, water parameter overlap, territorial needs, and schooling requirements before you buy new fish.