About PondPoise

A healthy goldfish or koi pond comes down to a handful of numbers: how much water it actually holds, how many fish that water can comfortably support, how fast the filter needs to turn it over, how much to feed on a given day, and how much to change out each week. Get those numbers right and the pond mostly takes care of itself. Get them wrong — even with the best intentions — and you end up chasing cloudy water, stressed fish, or an algae bloom that keeps coming back. PondPoise is built around getting those numbers right before they become a problem.

Rather than long articles you have to read end to end, the site is built around a set of small, single-purpose calculators, each aimed at one real pond-keeping decision. The Pond Volume Calculatorworks out how many gallons or litres a pond holds from its shape and dimensions — rectangular, round, oval, or an irregular naturalistic shape. The Fish Stocking Density Calculator checks your total fish length against your pond volume so you can see whether a pond is comfortably stocked, crowded, or has room for more, with separate guidance for goldfish and koi. The Filter Turnover Calculator converts your pond volume and a target turnover time into the pump flow rate, in gallons per hour, your filtration needs to keep up with the bioload. The Feeding Amount Calculatorscales a daily feeding amount to your fish’s total weight and the water temperature, since goldfish and koi eat far less — or not at all — once the water turns cold. The Water Change Calculator works out exactly how much water to remove and replace for a given percentage change, in gallons and in bucket-loads. And the Pond Liner Size Calculatorsizes the liner sheet you need to buy, from your pond’s length, width, and depth, before you break ground.

Alongside the calculators, the blog and learnsection explain the reasoning the tools rest on — how stocking density and filtration capacity interact, why water temperature changes what and how much to feed, and how goldfish, koi, and the other fish suited to an ornamental pond differ in the space and care they need. Every explanation is written from scratch, in plain language, for people who actually keep fish in a garden pond.

A few things worth stating plainly. PondPoise is an independent site and not affiliated with any pond-supply manufacturer, hatchery, or veterinary body. It is supported by advertising, which is how the tools stay free with no account required. The calculators are planning aids built on widely used pond-keeping rules of thumb — they help you plan stocking, filtration, feeding, and maintenance, but every pond, climate, and fish community is different, and nothing here is veterinary or medical advice for a fish that appears sick or injured; for that, a qualified aquatic veterinarian is the right call. If a tool result looks off, or there’s a calculator you wish existed, the contact page is the place to tell us.