Sowing the Seeds of Tomorrow

Fish Stocking Calculator

How many fish your media can actually filter

12fish

maximum mature fish this system can support

at 1 lb each · 11.97 lb total supported load

1 Your grow bed

Wet media zone — length × width × depth

length (ft)

width (ft)

wet depth (ft)

Wet depth is only the saturated zone the bacteria colonize — not the dry top layer. 10″ media with a 2″ dry cap = 0.67 ft wet.

2 Your media

Media type (this is the lesson — watch the fish count move)

3 Your fish plan

Target BSA per pound of mature fish (safety margin)

Higher number = more cushion, healthier margins, fewer fish. The 100 ft²/lb rule is the conservative gold standard for a stable first system.

Harvest weight per fish (lb)

= The math, step by step

Total media volume (L × W × D)6.64 ft³

× media surface area (SSA)95 ft²/ft³

= Biological Surface Area (BSA)631 ft²

÷ target per pound100 ft²/lb

= Supported mature fish load6.3 lb

Why media is the whole game: swap Hydroton for large river rock in the same exact bed and your fish capacity drops by more than half — same water, same space. The bacteria don't live in the water. They live on the surface of the media. More real estate, more fish. This is the way.

Media SSA values are widely-used planning figures from the aquaponics community, not lab constants. Verify against your actual media and cycle by your test kit.

Credit where it is due

This calculator is built on the work of Murray Hallam, the Australian aquaponics pioneer behind Practical Aquaponics in Queensland. The biological surface area approach to stocking density, the idea that your media, not your water volume, sets your fish ceiling, comes from his teaching and his research.

If you are serious about building a system, go to the source: aquaponics.net.au. His video series Aquaponics Made Easy, Aquaponics Secrets and DIY Aquaponics are where a lot of us started.

Any errors in this implementation are ours, not his.

More coming to this page

System types: media bed, deep water culture, NFT, and the CHOP layout
Fish selection for Northeast Ohio, tilapia, bluegill, catfish, and trout
Cycling a new system and what the test numbers mean
Pairing aquaponics with a microgreens operation

Learn it hands on

Aquaponics is part of the Foundry curriculum at Sowing the Seeds of Tomorrow.
Apply to the Foundry →

Sowing the Seeds of Tomorrow
4155 East 97th Street, Cleveland, OH 44105
keith@stsot.org | 216-576-5435

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