Beginner aquarium guides

53 guides, in the order a first tank needs them. Each one answers one question and commits to the answer.

Water & Cycling

The nitrogen cycle, test numbers, and fixing bad water. 7 guides.

Water & Cycling14 min
How to Soften Aquarium Water: Lower GH Without Crashing pH
How to soften aquarium water: mix RO or distilled with tap at a measured ratio to lower GH. Get the formula, and why softeners and almond leaves fail.
Water & Cycling10 min
How to Lower Nitrates in a Fish Tank (and Keep Them Down)
To lower nitrates in a fish tank, change 50% of the water, then size your weekly change to fit. The tap water trap, the maths and which removers work.
Water & Cycling11 min
How to Lower Nitrites in a Fish Tank: What to Do Today
To lower nitrites in a fish tank, change 50% of the water today and add a little aquarium salt to block it. Then fix the cause. Exact doses, sourced.
Water & Cycling6 min
Why Do My Fish Keep Dying? Work Out When, Then Why
When fish keep dying one after another, the timing names the cause: a new tank, a water change, new fish or a neglected tank. How to find yours and stop it.
Water & Cycling4 min
Fish Lying on the Bottom of the Tank: Test the Water First
A fish lying on the bottom of the tank is usually reacting to the water: ammonia, nitrite, temperature or oxygen. What to check first and what to do today.
Water & Cycling4 min
Can You Use Distilled Water in a Fish Tank? Not on Its Own
Can you use distilled water in a fish tank? Not by itself — it has no minerals and cannot hold a stable pH. Use it for top-offs and to soften hard tap water.
Water & Cycling3 min
Nitrogen Cycle for Beginners: Why You Wait Weeks for Fish
Ammonia, nitrite and nitrate in plain English — how to run a fishless cycle step by step, and the one test that tells you the tank is ready for fish.

What you'll find here

These guides follow the order you actually need them in: choosing a tank and working out what it really costs, the equipment that matters (filter, heater, light, substrate) and what you can skip, the nitrogen cycle and how to run a fishless cycle properly, then stocking (beginner-friendly fish, easy live plants) and the maintenance routine that keeps it all stable.

Every guide is written by a named human author who keeps tanks, gives you the numbers to test against rather than vague advice, and gets updated when better information turns up. Read more about our editorial standards.

Water & Cycling

How to Soften Aquarium Water: Lower GH Without Crashing pH

How to Lower Nitrates in a Fish Tank (and Keep Them Down)

How to Lower Nitrites in a Fish Tank: What to Do Today

Why Do My Fish Keep Dying? Work Out When, Then Why

Fish Lying on the Bottom of the Tank: Test the Water First

Can You Use Distilled Water in a Fish Tank? Not on Its Own

Nitrogen Cycle for Beginners: Why You Wait Weeks for Fish

What you'll find here