Start Here: Your First Aquarium

The short version: buy a slightly bigger tank than you think you need, cycle it before any fish arrive, test the water weekly, stock slowly, and feed less than you want to. Everything else is detail.

Buy the right things first

Counter-intuitively, a bigger tank is easier, not harder. More water means mistakes dilute instead of spiking, and temperature and chemistry drift slowly enough for you to notice and respond. If you can, start at 20 gallons (about 75 litres) or larger — tiny tanks are the expert-mode option, not the beginner one.

Your core shopping list is short:

• The tank — 20 gallons or more, on a stand that can genuinely take the weight.
• A filter — its real job is housing the beneficial bacteria that keep water safe, not just catching debris.
• A heater — tropical fish need stable warmth; stability matters more than any exact number.
• A liquid test kit — one that reads ammonia, nitrite, nitrate, and pH. You will use it every week.
• Dechlorinator — tap water treatment, used every single time new water goes in.

Notice what is not on the list: fish. They come weeks from now, and that wait is the difference between a tank that works and one that quietly fails.

Set up and cycle — with no fish in the tank

Rinse everything in plain water, add your substrate and decor, fill the tank, dechlorinate, and get the filter and heater running. Then comes the step most new keepers skip: the cycle.

An aquarium needs a colony of beneficial bacteria that converts fish waste (ammonia) into nitrite and then into far-less-harmful nitrate. Growing that colony takes several weeks, and doing it before fish arrive — a fishless cycle — means no animal ever has to live in toxic water while you wait. Our guide Cycle Your Tank Safely (No Fish Needed) walks through it step by step. If you read only one other guide, make it that one.

Learn what the numbers mean

You do not need a chemistry degree — you need four numbers:

• Ammonia and nitrite — both toxic; in a cycled tank they should read zero.
• Nitrate — the end product that slowly builds up; water changes keep it in check.
• pH — a stable pH your fish are used to beats endlessly chasing a "perfect" one.

Water Chemistry Basics (pH, KH, GH) explains what is actually happening in the water, and Water Tests Made Easy: What the Numbers Mean turns your test results into decisions.

Choose fish that actually fit

Pick fish for the tank you have, not the one you wish you had. Check the adult size, temperament, and group needs of every species before you buy — plenty of common shop fish outgrow small tanks or bully their neighbours. Then stock slowly: add a few fish, wait a week or two while testing the water, and only add more once ammonia and nitrite stay at zero.

Stocking Guide: Choose Compatible Fish covers how to build a community that works, and the Stocking Planner tool and Build My Tank wizard on this site let you sanity-check a plan against your actual tank size before you spend anything.

Feed lightly

Overfeeding is the most common avoidable beginner mistake. Feed once or twice a day, only as much as your fish finish within a couple of minutes, and remove anything left over — uneaten food breaks down into the same ammonia you worked so hard to eliminate. A skipped day now and then does healthy fish no harm. Feeding Without Polluting Your Tank goes deeper.

Settle into a weekly routine

A stable tank runs on a boring, repeatable rhythm:

• Test the water once a week and note the results.
• Do a partial water change — around a quarter of the volume — with dechlorinated, temperature-matched water.
• Rinse filter media, when it needs it, in the tank water you removed — never under the tap, which kills your bacteria.
• Watch your fish at feeding time; behaviour changes are your earliest warning sign.

New Tank Plan: First 90 Days lays this out week by week for the whole stabilisation window.

When something goes wrong

At some point a fish will look off or a test will read high. Do not reach for a bottle of treatment first — test the water, because most problems trace back to it, and a partial water change is the safest first response to almost any bad reading. Emergency Help: First 60 Minutes gives you a calm checklist for exactly what to do, in order.

AquaLens can track all of this from your phone — cycle progress, test results, stocking, and feeding reminders — and the AquaLens App Handbook covers every feature when you are ready for it.