Keeping your tank alive on vacation
A healthy tank runs itself for two weeks without intervention. Pre-trip prep, auto feeder settings, and what actually goes wrong while you're away.
A stable, established aquarium can go two weeks without attention. Fish can handle a week without food. The filter keeps running. The heater holds temperature. The light timer cycles on and off. Most vacation disasters happen not because the owner left, but because a well-meaning house-sitter overfed the tank.
Before you leave
Do a water change. Do your normal weekly water change 1-2 days before departure. Starting with clean water gives the tank the best possible buffer for the days when nobody's doing maintenance.
Clean the filter. If the filter is due for a rinse, do it before you go. A partially clogged filter that loses flow while you're away can cause oxygen and ammonia problems. Clean media with good flow buys you an extra 2-3 weeks of hands-off time.
Check equipment. Make sure the heater is working and set correctly. Confirm the filter is running at full flow. Check that the light timer is set properly (6-8 hours on, the rest off). If you have a CO2 system, either leave it running on its normal solenoid timer or turn it off entirely; turning it off is safer than risking an unmonitored leak while you're gone.
Lower the water level slightly. This sounds counterintuitive, but if you have an HOB filter, a water level that drops 2-3 cm from evaporation can cause the return waterfall to splash loudly or, worse, cause the pump to lose prime. Top off to the maximum level before leaving. In dry climates or heated rooms, evaporation over two weeks can be significant.
Reduce feeding for a few days before departure. This slightly lowers the bioload going into the vacation period and gives the fish a chance to clean up any remaining food in the tank.
Feeding while you're gone
One week: don't feed at all. Healthy adult fish tolerate a week without food easily. They're cold-blooded, they don't expend energy maintaining body temperature, and their metabolic rate is low. In a planted tank, they'll graze on biofilm, algae, and microorganisms. Wild fish go through irregular feeding periods naturally. One week of fasting won't harm them.
Fry and very young fish are the exception. They need frequent feeding and shouldn't be left unfed for more than 2-3 days.
Two weeks: auto feeder or very light feeding schedule. Electronic auto feeders (Eheim, Fish Mate, or similar) dispense a measured amount of dry food on a timer. Set it to feed once per day with a small portion. Test the feeder for several days before you leave to make sure the portion size is right and the mechanism doesn't jam. Load it with pellets or granules rather than flake; flakes clump and stick in the mechanism. Tape over any part of the mechanism that could allow the entire hopper to dump at once; a full dump of food into the tank while you're away can cause an ammonia spike severe enough to kill fish.
The house-sitter risk. A well-meaning person who doesn't keep fish will almost certainly overfeed. The instinct is to be generous. "They look hungry" is what everyone says about fish, because fish always look like they're begging for food. If you must ask someone to feed, pre-portion the food into small daily baggies or containers labeled by day. Tell them explicitly: one portion per day, no more, even if the fish "seem hungry." Nothing extra. Overfeeding is the number one cause of vacation tank crashes, more common than equipment failure.
What actually goes wrong
Power outage. A brief outage (under 6 hours) is harmless. The filter bacteria survive without flow for 24-48 hours as long as the media stays wet. Temperature drops slowly in a large tank; a 200-liter tank in a heated room loses about 1°C per hour with the heater off. A 12-hour outage in winter is the scenario that kills fish: temperature drops into the danger zone, filter bacteria start dying, and ammonia rises when everything restarts.
If you live somewhere with unreliable power, a battery-powered air pump on a USB power bank provides emergency aeration. It's cheap insurance.
Heater failure. A stuck-on heater cooks the tank. A stuck-off heater chills it. There's no remote monitoring solution that's worth the cost for most hobbyists, but setting the heater a degree below your target (rather than right at it) reduces the risk of overheating. If you're paranoid, use two smaller heaters instead of one large one. If one fails on, the other isn't powerful enough to overheat the tank by itself. If one fails off, the other still provides partial heating.
Evaporation. In a hot or dry environment, a tank can lose 5-10% of its volume per week to evaporation. Two weeks of unchecked evaporation in a small tank exposes the heater, drops the HOB filter's intake below water level, and concentrates minerals and waste. In larger tanks (200+ liters) this is less critical. In nano tanks (under 40 liters), it's a real risk. Top off before you leave and consider covering the tank partially to reduce evaporation rate.
The two-week rule
Two weeks is the practical maximum for leaving a stable tank unattended. Beyond that, nitrate accumulates, evaporation compounds, and any small problem (slow leak, dying fish, clogged filter) has too long to escalate. For trips longer than two weeks, ask someone to do a partial water change at the halfway point. A fishkeeping friend is ideal. A house-sitter with printed instructions and pre-portioned food is acceptable. YouTube tutorials sent to a non-fishkeeping friend are a last resort, but better than nothing.
What to do before you leave
3-5 days before departure:
Test water parameters (pH, ammonia, nitrite, nitrate). If anything is off, address it before you leave so the tank enters vacation in stable condition.
Do a 25-30% water change. This gives the tank a fresh start with lower nitrate and replenished minerals.
Clean the filter if it's due. Don't clean it the day before leaving (in case something goes wrong); do it 3-5 days out so the bacterial colony has time to recover.
Remove any dead or dying plant material and trim overgrown plants. Decomposing plant matter consumes oxygen and can spike ammonia.
The day before:
Set the light timer. Reduce the photoperiod to 6-8 hours per day during your absence (from the usual 8-10). Less light means less algae growth and less photosynthetic demand on the CO2/nutrient balance.
Top off the water to the full line. Evaporation over a week or two can lower the water level noticeably, reducing filter flow and increasing pollutant concentration.
Load the auto-feeder if you're using one and run a test cycle to verify the portion size. Too much food per cycle is the most common auto-feeder problem.
What to tell your fish-sitter
If someone is checking on the tank while you're away, give them specific, simple instructions. Don't leave it to their judgment. A well-meaning but inexperienced sitter can cause more harm than an unsupervised tank.
Write it down: "Feed one pinch from this container, once per day. Don't add anything else to the tank. If a fish looks sick, text me a photo. Do not add medication. If the power goes out, plug in the battery air pump from the cabinet next to the tank."
Pre-portion the food into daily servings (small ziplock bags or a pill organizer with one compartment per day). This prevents overfeeding, which is the number one way sitters crash a tank.
The water change calculator can help you determine how much of a water change to do before leaving based on your stocking level and trip duration.