Planning a new aquarium
Size the tank, then check glass thickness, substrate depth and heater wattage before you buy or build anything.
EinstApp is a free collection of 30 aquarium calculators and 68+ in-depth guides — tank volume, heater size, filtration, CO2, reef dosing, stocking levels and more. No sign-up, no downloads: pick a calculator, enter your numbers, get your answer.
Most fishkeeping problems are really math problems. Here are the questions that bring thousands of aquarists to EinstApp every day — each one answered by a calculator in seconds.
Rectangular, bowfront or cylinder — get the true water volume in gallons and liters, accounting for substrate and displacement.
Aquarium Volume CalculatorCorrect wattage from your tank size and room temperature — no more guessing or dangerous swings.
Heater Size CalculatorSafe stocking levels based on adult size and bioload, not outdated inch-per-gallon rules.
Stocking Level CalculatorBubble count and saturation for planted aquariums, straight from your KH and pH readings.
CO2 CalculatorHit your target nitrate level with the right change size and frequency — calculated, not guessed.
Water Change CalculatorDose ammonia correctly, day by day, and know exactly when it is safe to add fish.
Fishless Cycle CalculatorEvery calculator is free, instant and mobile-friendly. Each one comes with a full guide that explains the formula, shows a worked example and lists the mistakes to avoid.
Tank dimensions, water volume, sumps, substrate and glass safety — every calculation you need before filling the tank.
Heaters, chillers, filters, UV sterilizers, lighting and running costs — sized correctly the first time.
Cycling, CO2, fertilizers, water changes and parameters — the invisible half of fishkeeping.
Salinity, two-part dosing, magnesium and reef chemistry for thriving corals.
Stocking levels, feeding, medication dosing and acclimation — keeping animals healthy.
Built by aquarists who got tired of conflicting forum answers. Here is what makes the tools different.
Every calculator uses the same formulas used by breeders, reefers and engineers — with the reasoning shown so you can trust the number.
Enter your measurements and the answer updates as you type. No waiting, no page reloads, no accounts.
All 30 calculators and 100+ guides are completely free. No paywalls, no premium tiers, no locked features.
Mobile-friendly pages designed to be used while you are measuring — phone in one hand, tape measure in the other.
Guides are tiered by experience: your first water change or two-part dosing on an SPS reef, both covered.
Each calculator is paired with an expert guide: the formula, a worked example, common mistakes and an FAQ.
From planning your first tank to running an advanced reef — every stage of the hobby has its own set of numbers to get right.
Size the tank, then check glass thickness, substrate depth and heater wattage before you buy or build anything.
Calculate water change size against your nitrate target, dose dechlorinator exactly, and size filter media properly.
Dial in CO2 from KH and pH, mix Estimative Index dry salts, and match lighting to your plants.
Convert salinity at any temperature, dose two-part in balance, and raise magnesium safely.
Dose medications by true tank volume, acclimate new fish on a timed drip schedule, and feed the right amount.
See what your aquarium really costs per month in electricity, and how much water your RO/DI system wastes.
Calculator-backed guides written for every level — from setting up your first tank to advanced reef chemistry. New articles are published every day.
Substrate depth controls cleaning effort, plant health, gas pockets and even nitrate export. Here's how deep each type of tank should run — and why.
6500K, 10000K, actinic — Kelvin ratings describe color, not plant growth. What the numbers mean, what plants actually absorb, and how to choose for eyes versus chlorophyll.
Carpet plants need soil, crypts need root tabs, anubias need nothing — the substrate ladder from bare glass to deep aquasoil beds, and which plants justify each rung.