DIY Pond Greenhouse: Wintering a 120-Gal Shell in Alabama

The Setup Works

120-gal preformed pond, 22" deep, 5 goldfish + fry, screen frame → add 6 mil plastic + de-icer = functional greenhouse. Alabama winters (zone 8a) rarely sustain deep freezes; this setup prevents surface sealing.

Key Optimizations

1. Raise filter/pump intake to 12" below surface — circulates cold top water, preserves warmer bottom refuge.
2. De-icer (100W) + aerator — dual gas-exchange insurance.
3. Vent on sunny days — plastic tents overheat fast (20°F+ spikes). Prop open or use zippered vents.
4. No feeding below 50°F water temp.
5. Monitor temp with min/max thermometer.

Plants & Fry

Hardy marginals survive. Fry need cover (floating plants, fine mesh). De-icer keeps small area open — fry congregate there.

Cost & Effort

~$50 plastic, $30 de-icer, $20 aerator. 30 min setup. Worth it for peace of mind.