Fasting tolerance varies by species + age. 3-7 days fasting is safe for: tetras, rasboras, danios, livebearers (guppies, platies, mollies), most barbs, corydoras (3 days max), most community fish. 10-14 days tolerable: oscars + larger cichlids, plecos (with driftwood to graze), goldfish, bettas, koi. They'll be fine for vacation. NEVER fast: fry under 2 weeks (need daily food, multiple times), mandarin dragonets (need constant copepod grazing), saltwater anthias (high metabolism), sensitive marine species. For vacations 7+ days: options: 1) feeder cube (slow-release block) - controversial because they cloud water if full bioload. 2) auto-feeder (Eheim Twin) with pre-portioned daily feedings. 3) ask a friend to feed every 2-3 days (small portions only - overfeeding kills more fish than fasting). For vacations 14+ days: auto-feeder mandatory + ATO + heater on Inkbird controller + email alerts via Apex/Inkbird WiFi. Bonus: a 2-3 day fast monthly is healthy for adult fish - clears digestive system, prevents constipation in bettas + livebearers.
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