You just filled your brand-new aquasoil tank, tested the water, and the ammonia reading is off the chart. Before you panic: this is normal, expected, and actually part of the design. Rich aquasoils like ADA Amazonia release a flood of ammonia as their organic nutrients break down — and cycling through that ammonia leach correctly is the difference between a tank that takes off and one that fights algae for three months.
This guide explains why the leach happens, how long it lasts, the exact water-change protocol to get through it, and how to know when you're safely cycled.
Why Aquasoil Leaches Ammonia
Aquasoil isn't just baked clay — it contains a substantial fraction of organic matter: the decomposed plant and soil material that makes it so fertile. Once submerged, bacteria begin breaking that organic matter down, and one of the first byproducts is ammonia (NH3/NH4+). Rich soils contain more organics, so they leach more ammonia, for longer.
This is deliberate, not a defect. The ammonia pulse:
- Kickstarts the nitrogen cycle aggressively — your filter bacteria get an abundant food source from day one, so the cycle establishes fast and robustly.
- Feeds early plant growth — plants uptake ammonium directly and preferentially; the leach is fertilizer.
- Suppresses early algae indirectly, because fast-growing plants fueled by abundant nitrogen outcompete algae for everything else.
Leaner soils like Fluval Stratum leach much less — a mild bump rather than a flood. Our Stratum vs Amazonia comparison quantifies the difference. But the protocol below works for any leaching soil; you just taper faster with leaner ones.
How Long the Leach Lasts
For a rich soil like ADA Amazonia, expect:
- Week 1–2: heavy leach — ammonia reads 2–8+ ppm. This is the peak.
- Week 3–4: tapering — ammonia drops toward zero as bacteria catch up and organics deplete; nitrite may spike as the second stage of the cycle kicks in.
- Week 4–6: typically resolved — ammonia and nitrite read zero 24 hours after a water change.
Variables that stretch or shrink the timeline: temperature (warmer cycles faster), filtration (more biomedia = faster), plant mass (heavy planting from day one absorbs a large share of the ammonia directly), and water change discipline (removing ammonia doesn't slow the cycle — the bacteria colonize surfaces, not the water column — so big water changes are pure benefit). Once the leach resolves, the soil enters its productive phase — typically 12–18 months of rich feeding before nutrients taper off (see our aquasoil exhaustion guide for what comes next).
The Startup Protocol: Dark Start vs Planted Start
There are two schools of thought, and both work. Pick based on your temperament.
Method 1: The dark start (patient, low-algae)
Set up substrate and hardscape, fill the tank, start the filter — but add no plants and no light for 2–3 weeks. Do large water changes (50–70%) every few days. Without light, algae can't establish; bacteria colonize the filter and substrate undisturbed. After ammonia reads zero, plant heavily and start the lights. The downside: you stare at an empty tank for weeks, and you miss the early window where plants could be using the leach as fertilizer.
Method 2: Plant heavily from day one (fast, classic ADA)
This is the traditional approach and the one we recommend for most planted-tank keepers:
- Plant as heavily as you can afford on day one — especially fast-growing stems. Every plant is an ammonia sponge. A sparsely planted Amazonia tank is an algae farm; a densely planted one is a rocket.
- Run lights at reduced intensity or shorter photoperiod (6 hours) for the first 2 weeks. Plants still photosynthesize; algae gets less opportunity.
- Water changes: 50% daily for the first week, every other day for week 2, then twice weekly until ammonia and nitrite read zero. Yes, daily. This is the price of rich soil, and skipping it is the #1 cause of new-tank algae disasters.
- Run CO2 from day one if you're injecting — it supercharges plant ammonia uptake.
- Hold off on liquid fertilizer for the first 4–6 weeks. The soil is providing everything; adding more just feeds algae.
- No livestock until ammonia and nitrite read zero — typically week 3–5. Then add animals gradually, not all at once.
A reliable pick here is Seachem Prime.
What NOT to Do During the Leach
- Don't add fish or shrimp early "to help cycle." The ammonia levels from rich aquasoil will kill or permanently damage them. A fishless cycle isn't optional here — it's mandatory.
- Don't use ammonia-locking chemicals as a substitute for water changes. Products that detoxify ammonia don't remove it; they just convert it to a form your test kit can't see while bacteria still process it. They don't reduce the leach and they complicate your readings.
- Don't vacuum or disturb the substrate. Churning the bed releases more organics and fines. Let it sit. Our substrate cleaning guide explains the hands-off approach aquasoil needs.
- Don't panic at brown diatoms in week 2–3. Diatoms are a normal new-tank phase fueled by silicates, not a sign your cycle failed. They fade as the tank matures.
- Don't add "bacteria in a bottle" and assume you're cycled. Bottled bacteria help seed the filter, but they don't neutralize a multi-week ammonia leach. They complement water changes; they don't replace them.
Testing: How to Know You're Through It
Test ammonia and nitrite (liquid test kit, not strips) every 2–3 days during the startup:
- Ammonia falling, nitrite rising: the cycle is progressing — first-stage bacteria are working, second stage catching up. Keep up water changes.
- Both reading zero 24 hours after a water change: you're essentially cycled. Do one more confirmation test the next day.
- Nitrate present and rising: the end product of the cycle — confirmation that the full chain (ammonia → nitrite → nitrate) is running.
Note that with heavy planting, you may never see a nitrite spike — plants uptake ammonia directly before bacteria convert it. That's fine; zero ammonia + healthy growing plants = cycled for practical purposes. When in doubt, the "add a small ammonia dose and check it's gone in 24 hours" test is definitive, but with aquasoil the soil itself is already dosing ammonia continuously.
A reliable pick here is API Freshwater Master Test Kit.
Special Cases
Cycling with a sand cap
Capping aquasoil with sand slows the leach slightly (less water flow through the soil surface) but doesn't eliminate it. Follow the same protocol; you may find the peak is a bit lower and shorter.
Shrimp tanks
Shrimp — especially caridina — are far more ammonia-sensitive than fish. Even after tests read zero, give a shrimp tank an extra 2 weeks of maturation before adding shrimp. Biofilm needs time to develop, and young tanks are unstable in ways test kits don't capture. Fluval Stratum's lighter leach is one reason it's popular for shrimp setups — and understanding how buffering substrates shape shrimp-tank chemistry helps you plan the tank beyond the cycle.
Reusing the protocol after rescaping
Disturbing an established aquasoil bed (major rescape, deep replanting) releases a mini-leach — trapped organics and fines hit the water column. It won't match the initial flood, but do a couple of large water changes after any major substrate disturbance and test for a few days.
Frequently Asked Questions
Is the ammonia leach harmful to plants?
No — it's beneficial. Plants uptake ammonium as a preferred nitrogen source, which is why heavily planted tanks cycle through the leach faster and with less algae. The only "harm" is to livestock, which is why the tank must be fishless until the leach resolves. Algae is the real competitor for that ammonia, hence the heavy planting and water changes.
Can I speed up the leach by doing even bigger water changes?
Up to a point. Large daily water changes (50–70%) are already the fastest practical method — they keep ammonia low enough that neither algae nor test-kit panic sets in. Beyond that, the organics break down on their own schedule; you can't rush decomposition, you can only manage its output. Warm water (78–80°F) during cycling modestly accelerates bacterial colonization.
My ammonia is still high at week 5. What's wrong?
Usually one of three things: water changes were skipped or too small during the peak (the most common cause), the tank is very lightly planted so nothing is absorbing ammonia, or filtration is undersized. Rarely, it's a bad batch of soil with exceptional organic content. Solution: resume aggressive water changes, add fast-growing stems, and verify your filter is actually flowing well.
Do I need to cycle if I'm using a lean soil like Stratum?
Yes, but it's gentler. Lean soils produce a mild ammonia bump that a standard fishless cycle handles in 2–4 weeks without the daily-water-change marathon. Still fishless, still test-driven — just less dramatic. Treat it as a normal new-tank cycle with a small head start on ammonia.
Can I put a used filter from another tank to skip the cycle?
Seeded filter media dramatically shortens the cycle — sometimes to days — because you're importing an established bacterial colony. It doesn't eliminate the leach itself (the soil keeps releasing ammonia for weeks regardless), but the bacteria process it immediately. Combined with heavy planting and water changes, seeded media is the closest thing to a shortcut that exists. Just don't add livestock on day one anyway; give it a week of testing first.
Embrace the Leach
The ammonia leach looks alarming on a test kit, but it's the engine of everything good about aquasoil: the fertility, the fast cycle, the explosive early growth. Respect it with heavy planting and disciplined water changes for a few weeks, and it pays you back with a tank that takes off like nothing else in the hobby. Fight it or ignore it, and you'll spend months wondering why your expensive soil grows only algae. The protocol is simple; the discipline is the hard part.