The 10 first-aquarium mistakes (and how to avoid them)
Published by Planète Pets · managing editor: Clément Lacaille · how our guides are written
Most first aquariums fail on the same 10 avoidable mistakes: a tank too small, a rushed setup, overstocking and overfeeding top the list. Knowing them before you buy makes the difference between a tank that stays stable for years and giving up after three months — here’s the list, in the order they’re usually made.
Contents · 5 sections
Which mistakes are made at purchase?
- 1. Choosing a tank that’s too small: below 54 litres, everything becomes unstable; the easy little tank is a myth.
- 2. Buying fish and aquarium the same day: the deadliest mistake, explained in our dedicated article.
- 3. Neglecting the stand: 100 litres weighs 130 kg fully equipped — a standard chest of drawers buckles.
- 4. Skimping on the heater: a model without a reliable thermostat (under 15 €) cooks or freezes the fish.
Which mistakes ruin the tank’s start-up?
5. Skipping the nitrogen cycle: 3 to 4 weeks of patience are non-negotiable before the first fish. 6. Washing the filter under the tap: chlorine kills the purifying bacteria; rinse the sponges in tank water. 7. Placing the tank in the sun: guaranteed algae and a sawtooth temperature — choose a wall with no window facing it, away from radiators.
Which mistakes creep in day to day?
8. Overstocking: the pet shop will happily sell 20 fish for 60 litres; the reality is half that, calculated in how many fish in an aquarium. 9. Overfeeding: two minutes of eating, once a day, one fasting day per week; the rest pollutes. 10. Changing all the water at the first problem: this reflex destroys the bacterial balance, as shown in our guide should you change all the water.
How much do these mistakes cost, and how much does avoiding them cost?
A full restart after a crash (lost fish, treatment, a new cycle) easily runs to 60-100 €, not counting the discouragement. Avoiding them costs almost nothing: a 15-25 € test kit, three weeks of patience and sensible stocking. All our start-up guides are on the fishkeeping hub.
Frequently asked questions
What is the most common mistake of all?
Buying the tank and the fish at the same time: without a nitrogen cycle, ammonia climbs within days and losses begin in the first week.
Can a beginner really succeed at the first attempt?
Yes: with a tank of 60 litres or more, three weeks of cycling and modest stocking, the success rate is excellent. Patience stands in for experience.
Do you need a test kit from day one?
Yes, it’s the tool that makes the nine other mistakes visible before they cost fish: 15 to 25 € for a liquid kit, the beginner’s best investment.
An accessory from our shop for this use: Ceramic pebble hide for shrimp and small fish (€20.90) · the whole shop
This guide is part of Planète Pets’s Fishkeeping universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.