Step 1: What do they eat in the wild?
Cichlids are mostly opportunistic carnivores. Plecos and otocinclus are herbivores that scrape algae. Bettas evolved as surface-feeding insectivores. Goldfish are omnivores. Match the formula’s diet type (carnivore, omnivore, herbivore) to your fish’s natural inclination.
Step 2: Where do they feed?
Surface feeders (bettas, gouramis) prefer floating pellets that stay on top long enough to be picked off. Mid-water feeders (most community tropicals) do well with slow-sinking pellets that drift through the column. Bottom feeders (plecos, corys) need wafers that settle on the substrate.
Step 3: How big is the mouth?
A pellet that is too big stresses small fish; one that is too small under-fills large ones. As a rule of thumb: pellet diameter should be roughly 30 percent of the fish’s mouth gape. A 1mm pellet works for most community fish; 2mm for adult cichlids and small koi; 3-4mm for adult koi, oscars, and large carnivores.
Common mistakes to avoid
Three traps catch most aquarists: (1) buying one bag of “fish food” for a multi-species tank — different fish have different needs, and the cheapest formula will hurt the species with the highest demands; (2) feeding a “just for goldfish” formula to all goldfish even though fancy goldfish need a softer pellet than comets; (3) sizing pellets up too aggressively as fish grow — bigger fish can usually still eat smaller pellets, but small fish never grow into oversized ones.
Special cases
Fry need a powder or nano pellet, not a regular formula crumbled up — the protein density in fry-specific feeds is calibrated for rapid growth. Breeding adults benefit from higher fat content and pigment-supportive ingredients (astaxanthin, krill). Aggressive feeders (oscars, arowanas) can be slowed down with sticks instead of pellets, which take longer to break apart.
When in doubt, take the Find Your Formula quiz on the home page — it walks you through these three questions in under a minute.
