Fish Food Calculator — How Much to Feed Fish (Aquarium Feeding)
How much should you feed fish? The 2-minute rule + 1–2 % body weight per day keeps ammonia low and fish lean. This fish food calculator sizes daily feedings for flake, pellet, and frozen food across any community aquarium.
Calculator
How to use the fish food calculator
- Enter tank volume + stocking — Tank gallons and rough fish count/size (small, medium, large).
- Select feeding type — Flake, pellet, or frozen — the calculator adjusts for water content.
- Read daily amount — Output is grams or pinches per feeding.
- Apply the 2-minute rule — Stop when food reaches the substrate. Err on the side of less.
Why overfeeding kills more aquarium fish than any disease
Uneaten fish food is one of the deadliest substances in a closed aquarium system. Every flake that falls past the mouth decomposes into ammonia (NH₃) within hours; nitrifying bacteria convert ammonia to nitrite (NO₂⁻), then nitrate (NO₃⁻). Ammonia at 0.25 ppm burns fish gills; at 1 ppm it's frequently fatal. A single episode of overfeeding can spike a newly cycled 10-gallon tank to 2+ ppm ammonia overnight and wipe out every inhabitant.
The 2-minute rule works because it caps input at roughly the same rate fish metabolize food. In the wild, most aquarium species graze continuously on small items — they never encounter a one-shot buffet. Feeding to satiation once and walking away mimics this: plenty eaten, nothing left over. The calculator's daily targets are based on published species-specific protein and calorie requirements (Merck Veterinary Manual, SRAC 5002) and assume you use the 2-minute rule as the final check.
Species-specific feeding differences
| Fish type | Daily % | Frequency | Notes |
|---|---|---|---|
| Tropical community (tetras, rasboras) | 1–2 % | 1–2×/day | Flake or micropellet |
| Goldfish (fancy) | 1–1.5 % | 2–3×/day | Sinking pellet — prevents SBD |
| Cichlid (adult) | 1.5–2 % | 2×/day | Carnivore or herbivore pellet |
| Pleco / catfish | 1–2 % | After lights-out | Algae wafer + veg |
| Discus (adult) | 2–3 % | 3×/day | Beefheart or pellet |
| Betta | 3–5 pellets | 1–2×/day | Betta-specific high-protein pellet |
Why you should fast your fish one day per week
A weekly 24-hour fast is a recognized practice among experienced aquarists and published in aquaculture veterinary literature. Reasons:
- Clears the gut — fish pass accumulated food and reduce nitrogenous waste output the following day.
- Prevents fatty liver — hepatic lipidosis is one of the top 3 causes of sudden death in well-kept aquarium fish, caused by chronic over-feeding of high-fat/low-fiber diets.
- Encourages natural grazing — on fast days fish actively hunt micro-fauna (copepods, biofilm) in the tank, which is mentally stimulating and covers micronutrients that processed foods miss.
- Prevents swim-bladder disorder in goldfish — the #1 trigger for SBD is over-feeding buoyant flake; fasting day resets their GI tract.
A 3–7 day fast (vacation) is also harmless for established tanks with adult fish. Avoid auto-feeders for short trips — the malfunction risk (stuck, over-dispense) is higher than the starvation risk.
Frequently Asked Questions
How much should I feed my fish each day?
The 2-minute rule: feed only as much as the fish can completely consume in 2 minutes, 1–2× daily. In practice this is 1–2 % of the fish's body weight in dry food per day. Overfeeding is the #1 cause of new-tank fish deaths — uneaten food decomposes into ammonia that burns gills and crashes the nitrogen cycle. Underfeeding a healthy adult fish by 10–20 % for a few days causes no harm.
What's the difference between feeding tropical fish vs. goldfish vs. cichlids?
Tropical community fish (tetras, barbs, rasboras) get flake or micro-pellet 2× daily at 2-minute volumes. Goldfish eat 2–3× daily but need sinking or pre-soaked pellets to prevent swim-bladder issues. Cichlids (Africans, discus, oscars) need 3× daily at growth stage, 2× as adults; carnivores get pellets + occasional frozen meat; herbivores need spirulina-based foods to avoid intestinal problems.
How often should I feed fish?
Adult community fish: 1–2× daily, with one fasting day per week to clear the gut. Juveniles and growing fish: 3–4 small meals per day. Nocturnal species (loaches, many catfish): feed after lights-out. Fasting is important — overweight fish develop fatty liver disease (hepatic lipidosis), the leading preventable cause of death in captive ornamental fish.
Can I feed frozen food instead of flakes?
Yes, and it's generally better. Frozen bloodworms, brine shrimp, daphnia, mysis shrimp and tubifex are closer to the natural diet of most aquarium fish than processed flakes. Thaw and rinse frozen portions before feeding to remove phosphate-rich thaw water. Rotate 3–4 frozen types with a high-quality flake/pellet base for complete nutrition.
I skipped a day — will my fish starve?
No. Healthy adult fish can comfortably fast 3–7 days with zero harm. Many experienced keepers fast deliberately one day per week. Auto-feeders should be sized conservatively if you're away; a week-long vacation rarely needs any feeder at all for an established community tank.
What are signs I'm overfeeding my aquarium?
Food reaches the substrate uneaten, persistent cloudy water, ammonia/nitrite test kit shows readings > 0 ppm, algae bloom (brown diatoms especially), fish with distended bellies, fat or “pineapple” scaling pattern. Cut feeding in half and do a 30 % water change if you see any of these.
How much fish food does a typical aquarium use per month?
A 20-gallon community tank with 10 small fish uses about 20–30 grams of dry flake per month — one 50 g container lasts 2–3 months. Heavy goldfish or cichlid stocking consumes 3–5× more. A 200 g container at $15 typically feeds a 40-gallon community for 8–12 months.
Sources & References
- [1]Feeding Ornamental Fish — Texas A&M Extension / SRAC
- [2]Feeding Your Aquarium Fish — VCA Animal Hospitals
- [3]Fish Nutrition — Species-Specific Guidelines — Aquarium Co-Op
- [4]Ornamental Fish Nutrition (USGS) — Merck Veterinary Manual
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