Protein Skimmer Size Calculator
The workhorse of saltwater filtration. Enter your tank size and bioload — we'll recommend the skimmer rating to shop for.
Calculate skimmer size
How skimmer sizing works
A protein skimmer removes dissolved organics before they break down into nitrate — it's the primary nutrient export on most reef tanks. Manufacturers rate skimmers by tank volume, but those ratings assume light stocking. This calculator multiplies your tank volume by a bioload factor:
- 1.0× tank volume — light bioload (few fish, light feeding)
- 1.5× tank volume — moderate bioload (typical community)
- 2.0× tank volume — heavy bioload (many fish or heavy feeding)
Shop for a skimmer whose rated capacity meets or beats the result — slightly oversizing is standard practice in the hobby.
Skimmer tips
- New skimmers need a 1–2 week break-in before they produce stable skimmate — don't judge it on day one.
- Skimmers only work in saltwater — freshwater doesn't foam, so they do nothing on freshwater tanks.
- Keep the water level in the skimmer chamber stable; an auto top-off helps enormously.
- Empty and clean the collection cup regularly — a neglected skimmer is just decoration.
Frequently asked questions
Do I need a protein skimmer for a saltwater tank?
For reefs and most marine tanks, yes — it's the most effective nutrient export you can buy. Very lightly stocked nanos with big weekly water changes can run without one, but that's the exception.
Can a protein skimmer be too big?
Mildly oversizing is fine and common. Grossly oversizing a tiny tank can strip too many nutrients and starve corals — match the rating to your bioload.
Hang-on-back vs in-sump skimmer?
In-sump skimmers are quieter, hold more water and are easier to tune. Hang-on-back models work well when you have no sump — just keep the water level steady.
Do protein skimmers work in freshwater?
No. Skimming relies on the surface tension of saltwater to form stable foam; in freshwater the bubbles collapse and nothing is exported.