250-Gallon Pond: Pump, Filter & Stocking Guide
Every key number for a 250-gallon pond in one place: a 250 GPH pump, a 9W UV clarifier, about 1 koi, 1 aeration diffuser, and 6.3 lb of salt at 0.3%.
Quick answer
A 250-gallon pond wants a pump near 250 GPH (buy rated ~325), a 9W UV clarifier in partial sun, about 1 koi or 5 goldfish, 1 aeration diffuser, and about 6.3 lb of pond salt for a 0.3% treatment. Tap any number below for the full breakdown.
250-gallon pond: every number
| Question | Answer |
|---|---|
| Pump flow (koi, once/hour) | 250 GPH (buy ~325) |
| UV clarifier (partial sun) | 9W |
| Koi stocking | ~1 koi |
| Goldfish stocking | ~5 goldfish |
| Aeration diffusers | 1 (Small air pump) |
| Pond salt at 0.3% | 6.3 lb |
This is the one-page system summary for a 250-gallon pond. Each figure below is computed from the same formulas in our calculators, and each links to a full answer with the table, context, and gear. At this volume the pond is below the usual koi minimum, so it suits goldfish best.
How the Numbers Fit Together
Circulation comes first: a pump near 250 GPH turns a 250-gallon koi pond over once an hour, and you buy one rated around 325 GPH to beat head and plumbing losses. A 9W UV clarifier polishes out green water, while 1 diffuser on a small-class air pump keep oxygen up. Stocking stays conservative at about 1 koi or 5 goldfish, because overstocking is the root of most water-quality trouble. Pond salt, when needed, runs about 6.3 lb for a 0.3% treatment.
Open Any Answer for the Full Breakdown
Each linked page below shows the computed number, a short table, the reasoning, and matched gear for a 250-gallon pond. Start with circulation and filtration, confirm your stocking, then layer in aeration and any salt treatment. If you are still planning the build, the pond volume calculator confirms your true gallons first, and the liner calculator sizes your EPDM and underlayment.
Core gear for a 250-gallon pond
The heart of your circulation.
Clears and prevents green water.
Track ammonia, nitrite, and pH.
Run your own numbers or keep exploring:
Pond Build & Maintenance Planner
Build planner, stocking planner, water-test log, and seasonal maintenance schedule, in one printable planner that keeps your pond healthy year-round.
Frequently Asked Questions
What pump and UV does a 250-gallon pond need?
Plan for a pump near 250 GPH (buy one rated around 325 GPH for head losses) and a 9-watt UV clarifier in partial sun. Both scale with your gallons, and full sun bumps the UV size up.
How many fish can a 250-gallon pond hold?
About 1 mature koi at 250 gallons each, or about 5 goldfish at 50 gallons each. It is below the 1,000-gallon koi minimum, so goldfish suit it better.
How much aeration and salt for a 250-gallon pond?
Run about 1 diffuser on a small-class air pump, hardest in summer. For a 0.3% salt treatment, add about 6.3 pounds of pure pond salt, gradually and predissolved.
Planning or running a pond?
Use our free calculators and guides to get every number right.
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