Fish checklist

Before you go

• Cycle the tank first. Four to six weeks, until ammonia and nitrite both read zero and nitrate is present. Adding fish to an uncycled tank is the commonest way to kill them.
• Buy a liquid test kit, not strips.
• Match the species to your water. Hardness and pH matter more than most shops let on.
• Check the adult size. A common plec reaches 45cm; a goldfish needs far more water than a bowl.

On the day

• Fins held out, not clamped. No white spots, cotton-wool patches, red streaks or ulcers.
• Swimming normally, not gasping at the surface or sitting on the bottom.
• Clear eyes, no bloating, no wasting behind the head.
• Look at the whole shop system, not just your tank: dead fish in a neighbouring tank on shared filtration means every fish in that system is exposed.
• Ask what the shop's water parameters are, so you can match them.

Transport and introduction

• Bag them with plenty of air, keep them dark and warm, go straight home.
• Float to equalise temperature, then drip-acclimatise over 30 to 60 minutes.
• Quarantine new fish for two weeks if you already have a stocked tank.

Walk away if

• The shop's tanks are visibly ill, dirty or overstocked.
• You are told a fish will "grow to the size of the tank". It will not; it will be stunted and die early.
• You are sold fish on the day you set the tank up.