What This Part Covers
Part 1 laid out the theory behind the Walstad Method. This part walks through actually setting up the tank — supplies, building the soil layer, choosing plants, and caring for the tank through its first few weeks.
Supply Checklist
- Tank (45cm/12 gallons minimum recommended; beginners benefit from going larger for stability)
- Organic soil (plain potting soil, no added fertilizer or perlite)
- Cap material (sand or fine gravel, 2-3cm deep)
- A generous supply of fast-growing stem plants
- A gentle sponge filter or low-flow filter
- Low to moderate light
- Thermometer, net, siphon (optional)
Choosing your soil
Avoid fertilized potting mixes or anything containing perlite. Stick to plain organic soil (peat-based, no additives) — this keeps the initial ammonia spike within a predictable, manageable range.
Building the Soil Layer
- Spread a 2-4cm layer of organic soil evenly across the tank bottom.
- Cap it with 2-3cm of sand or fine gravel so the soil never touches the water directly.
- Slope it shallow at the front, deeper at the back for both perspective and drainage.
- Mist the soil surface lightly with water before capping to keep it from floating up.
Plant Selection — The Key to Early Stabilization
Early on, a Walstad tank needs “workhorse” plants that can rapidly absorb the surge of nutrients the soil releases. Floating and fast-uptake stem plants that feed through leaves rather than roots work best.
- Water Sprite
- Najas guadalupensis (guppy grass)
- Hornwort
- Floating plants like duckweed or water lettuce (cover only 30-50% of the surface to avoid blocking too much light)
Plant these as densely as possible from day one — density is what lets plants outcompete algae for available nutrients.
Lighting — Less Is More
Without injected CO2, too much light lets photosynthesis outpace the tank’s natural CO2 supply, and algae are the ones that benefit from the mismatch. Start with 6-8 hours a day of low-to-moderate LED light and adjust based on whether algae appears.
Setup Sequence
- Clean the tank → lay the soil layer → add the cap
- Place hardscape (driftwood, rocks)
- Fill carefully (use a plate or plastic sheet to break the water stream and keep the soil from floating)
- Plant densely with your prepared stock
- Install the filter, heater, and light, then start the tank
The First Few Weeks — Understanding the Die-Off Period
Expect cloudy or faintly brown water for the first 1-3 weeks. This is a normal “die-off” period where soil microbes bloom and then settle back down.
What to do during this period
Don’t do water changes during this window — that’s the whole point. Instead, cut back on lighting hours and hold off on adding fish until the water clears. Rushing it only destabilizes the cycle again.
Coming Up in Part 3
Part 3 covers the common problems — algae, odor, melting plants — that show up over months of actually running a Walstad tank, and how to handle them.