90-Gallon Low-Tech Walstad Aquascape (Beginner)
A 90-gallon Walstad-method tank: a nutrient soil base under a cap, heavy planting, and a system built to look after itself. It is a proper display tank with room to build depth. No CO2 and no dosing regime — slower to fill in, far more forgiving, and cheaper to run. 10 plant species, Malaysian Driftwood, and 7 livestock groups checked against each other for compatibility — every quantity below sized to 90 gallons and every plant chosen for a beginner.
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Hardscape — what to buy and how to place it
Malaysian Driftwood is dense and dark, with knotted, worn, gnarled forms. It leaches tannins strongly, so expect an amber tint for the first few months. That tint is harmless and slightly acidic, and many people want it — if you do not, run activated carbon or lift a little more water at each change. It is dense enough to sink straight away, which makes it the least fussy wood here to place. Give it a scrub and a long soak first to take the worst of the initial tannin release out of the tank.
At 90 gallons, plan on seven or more pieces in clearly unequal sizes. An odd count is easier to compose, and one piece should obviously lead — a group of similar-sized pieces spread evenly across the tank is the most common way a first scape goes flat.
Whatever you place, keep it off the soil layer where you can. This method depends on an undisturbed nutrient base doing its work, so heavy hardscape pressed into the soil is working against the tank rather than with it.
Substrate
Aqua soil or capped organic base, capped with fine natural gravel/sand cap, built to about 2.5–3.5" and sloped higher at the back. A nutrient base keeps low-tech plants fed; cap with fine gravel. Slope higher at the back.
A capped nutrient base is the engine of a low-tech tank, so the one rule is to leave it alone. Vacuum the cap, never the layer beneath it — driving a siphon down into the base releases everything it has been quietly storing and can gas a tank in an afternoon.
Because this plan carpets the foreground, keep the front of the substrate shallow and level — around an inch is plenty — and save the depth for the back. Carpets are planted into a flat bed in small clumps a couple of centimetres apart, and they spread sideways to meet; planting them dense enough to look finished on day one wastes plants and traps debris.
Spiral Cryptocoryne, Echinodorus amazonicus, Amazon Sword and Echinodorus 'Ozelot' are root feeders rather than water-column feeders, so they want depth and a root tab more than they want dosing. Give that part of the bed the extra depth.
At 90 gallons the substrate is a real purchase, not an afterthought — budget for it early and buy it all at once, because a bed topped up later with a different bag rarely matches.
Plant list & placement
Plant back to front, into damp substrate with the tank only part-filled — it is far easier than fighting buoyancy in a full tank. Hornwort is the tallest thing in this plan at around 24", so it sets your back row and everything else steps down in front of it.
Fairy Moss (Azolla) is the fast grower here — tiny fern-like floater; reddens in strong light, fast nutrient sponge. Expect to be cutting it every two or three weeks once it establishes. Top the stems, replant the healthy tops in the same group and discard the old bases; a stem bed replanted from tops stays dense, while one left to grow on goes bare at the bottom.
Fairy Moss (Azolla) and Java Fern (standard) are epiphytes and must never be buried. Tie or glue the rhizome onto your hardscape and leave it fully exposed — a buried rhizome rots, and it is the single most common way a beginner loses an Anubias or a Java fern. Only the roots may touch the substrate.
Fairy Moss (Azolla) and Hornwort sits on the surface, which does two useful things and one inconvenient one: it shades the tank, which calms most fish and suppresses algae, and it strips nitrate fast — but it also cuts the light reaching everything below, so thin it out by hand whenever it covers more than about half the surface.
Group the stems rather than spacing them out. Spiked Water Milfoil, Echinodorus amazonicus and Amazon Sword each want to be planted as a block of stems an inch or so apart, cut to slightly different heights so the group fills in with a rounded top instead of a flat hedge.
Every plant here is a hardy, forgiving species. None of them need CO2 to survive, and all of them recover from being neglected for a fortnight — which is the right way to start, because the tank should be teaching you the routine rather than punishing you for missing it.
Stocking
This stocking is built to spread through the tank rather than crowd one layer: Lambchop Rasbora and Black Neon Tetra share the open middle water, Pearl Gourami works the surface and Kribensis works the floor. A tank where every fish occupies the same band looks half-empty even when it is fully stocked, and the fish themselves compete more.
Keep Lambchop Rasbora in 8 or more and Black Neon Tetra in 6 or more. These are not decorative numbers — a shoaling fish kept in threes spends its life stressed, colours down and hides, and people then conclude the species is dull. The counts in the list above are already scaled to this tank.
Pearl Gourami is the centrepiece. Elegant, peaceful larger gourami with lace-like pattern; classic community centerpiece.
Blue Mystery Snail, Mystery Snail and Gold Mystery Snail are the clean-up crew, and in a planted tank they earn their place — grazing biofilm and soft algae off the hardscape and leaves faster than you can. Add them last, once the tank has some algae to eat, and drip-acclimatise rather than dumping the bag in.
- Lambchop Rasbora — Keep Lambchop Rasbora in a group of at least 8 — kept in ones or twos they get stressed, shy, and nippy.
- Pearl Gourami — Pearl Gourami is territorial/solitary — best kept as a single specimen.
- Kribensis — Kribensis is territorial/solitary — best kept as a single specimen.
- Black Neon Tetra — Keep Black Neon Tetra in a group of at least 6 — kept in ones or twos they get stressed, shy, and nippy.
The largest fish here is roughly 3.6× the length of the smallest, which is the point at which size alone starts to matter — that gap was checked against mouth size and feeding behaviour, not just temperament. Every pairing was run through Skapelab’s compatibility engine and anything returning even a caution was swapped out rather than published. Check any substitution you make there before you buy.
Equipment
| Category | Recommendation | Notes |
|---|---|---|
| Filtration | Eheim Professionel 4+ 600 | ~$380–470 |
| Lighting | Finnex Stingray 2 48" | ~$46–68 |
| Heating | Oase BioMaster Thermo 600 (integrated) | Included with Oase BioMaster Thermo 600 (~$360–450) |
| Substrate | CaribSea Super Naturals Torpedo Beach Sand | ~$18–28 |
| Fertilizer | Seachem Flourish Comprehensive 250ml | ~$8–14 |
| Testkit | API Freshwater Master Test Kit | ~$28–42 |
| Water treatment | Seachem Prime 500ml | ~$12–20 |
| Bacteria | Seachem Stability 250ml | ~$8–14 |
What the first two months look like
| Week 1 | Hardscape in, planted, filled and running with no livestock. Start the photoperiod short — six hours is plenty — because the plants are not yet growing fast enough to use more, and the surplus goes to algae. Your Malaysian Driftwood sinks on its own, so it can simply be placed — but it will start tinting the water this week. |
| Weeks 2–4 | Cycling, and the ugly phase. Brown diatom dust on the glass and hardscape is normal in a new tank and passes on its own once silicates are used up. Some plants will melt back and regrow in their submersed form — that is conversion, not death, so trim the mush and leave the roots. Do not stock until ammonia and nitrite both read zero. |
| Weeks 4–6 | Stocking begins, a few animals at a time with a fortnight and a water test between additions. The first real trim happens somewhere in here, and the tank stops looking newly planted. |
| Months 2–3 | The soil settles into balance and the tank starts running itself. This is the point where a Walstad tank rewards having been left alone: stable, undemanding, and needing less from you each month rather than more. |
Care schedule
| Daily | Feed lightly — as much as they clear in a minute or two — and take ten seconds to count heads and look at the plants. |
| Weekly | 27% water change — about 24 gallons — using a tap-fed water changer — at this volume buckets stop being realistic. Wipe the glass, vacuum the open substrate only, and dose a light all-in-one fertiliser. Trimming is occasional rather than weekly at this growth rate. |
| Monthly | Rinse filter media in old tank water — never under the tap, which kills the bacteria colony you spent six weeks growing. Test KH, GH, pH and nitrate. On a tank this size also check the seals and the stand for damp, because a slow leak here is a floor problem, not a tank problem. |
| Every few months | Thin the slow growers back hard once or twice a year, divide anything that has outgrown its spot, and top up root tabs around the heavy feeders. |
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