125-Gallon High-Tech Iwagumi Aquascape (Advanced)
A 125-gallon Iwagumi: a few stones, one carpet, and a great deal of deliberate empty water. It is a large display tank, wide enough that the layout has to work across the whole span. Pressurised CO2, active soil and real light — faster growth, more colour, and a tank that needs you every week. 1 plant species, Dragon Stone, and 4 livestock groups checked against each other for compatibility — every quantity below sized to 125 gallons and every plant chosen for an advanced.
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Everything below is generated for this 125-gallon Iwagumi build — 1 plant, 4 livestock groups, and gear sized to 125 gallons. The studio does the same for your tank, free.
Hardscape — what to buy and how to place it
Dragon Stone is warm ochre and deeply pitted, full of hollows and honeycombed pockets. Dragon Stone is baked clay and chemically inert, so it will not move your pH or hardness in either direction. Rinse and scrub it hard before it goes in — dry Ohko sheds a fine clay dust that will cloud the water for days. The hollows are planting pockets: press moss or a small epiphyte into them and the stone disappears into the scape as it grows.
At 125 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.
The discipline in Iwagumi is what you leave out. Every stone should look like a fragment of the same broken boulder — same colour, same texture, same direction of grain — and the open carpet between them is doing as much work as the stone is. If you are tempted to add a fourth stone to fill a gap, the gap is usually the point.
Substrate
Aqua soil (e.g. ADA Amazonia / UNS Controsoil), built to about 3–4" and sloped higher at the back. Active soil buffers soft, slightly acidic water and feeds roots. Slope higher at the back for depth.
Fresh aqua soil leaches ammonia for the first one to three weeks. That is normal and it is also why you do not stock a high-tech tank early: run it, change a good volume of water two or three times in that first fortnight, and wait for ammonia and nitrite to read zero before any livestock goes in.
The whole floor of this tank is Micranthemum sp. Belem, so the substrate contour IS the layout — there is no background planting to hide a flat bed. Build a real slope from front to back and let the carpet run up and over it; that rise is what gives an otherwise open tank its depth. Plant in small clumps a couple of centimetres apart and let them spread sideways to meet, rather than packing them in to look finished on day one.
At 125 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. Micranthemum sp. Belem is the tallest thing in this plan at around 2", so it sets your back row and everything else steps down in front of it.
Micranthemum sp. Belem is the fast grower here — tiny round-leaved carpet plant, smaller than Monte Carlo. Forms a very dense, bright green carpet. Requires high light, CO2, and frequent trimming. One of the most demanding carpet plants. Expect to be cutting it weekly 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.
Micranthemum sp. Belem is the demanding species in this plan, which is why it appears at advanced level: it needs stable CO2, consistent dosing and real light, and will show you the moment any of the three slips.
Stocking
This stocking is built to spread through the tank rather than crowd one layer: Chili Rasbora, Chocolate Gourami and Black Neon Tetra share the open middle water and Hongsloi Apisto 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 Chili 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.
Chocolate Gourami is the centrepiece. Delicate blackwater mouthbrooder for experts; needs warm, very soft acidic water.
- Chili Rasbora — Keep Chili Rasbora in a group of at least 8 — kept in ones or twos they get stressed, shy, and nippy.
- Chocolate Gourami — Keep Chocolate Gourami in a group of at least 4 — kept in ones or twos they get stressed, shy, and nippy.
- Hongsloi Apisto — Hongsloi Apisto 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 | Twinstar 1200SP | ~$720–860 |
| Co2 | GreenLeaf Aquarium GLA Regulator + 20lb Cylinder | ~$400–510 |
| Heating | Oase BioMaster Thermo 600 (integrated) | Included with Oase BioMaster Thermo 600 (~$360–450) |
| Fertilizer | Estimative Index DIY NPK Dry Ferts Kit | ~$28–45 |
| 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. CO2 comes on an hour before the lights and off an hour before they go out; aim the drop checker at a green, never yellow. Keep the photoperiod short, around six hours, while the plants root. |
| 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; the fresh soil is also still releasing ammonia, so keep changing water. 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 carpet should be visibly running now; resist raising the light to hurry it. |
| Months 2–3 | The scape fills in and the routine settles into the schedule below. On a tank this size, get the maintenance rhythm fixed now — a large tank is very stable until it is not, and by then it is a large problem. |
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. Check the drop checker is green before the lights come on. |
| Weekly | 40% water change — about 50 gallons on this tank — using a tap-fed water changer — at this volume buckets stop being realistic. Dose your macros and micros after the change, not before. Wipe the glass and check the CO2 cylinder pressure. |
| 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 | Replace the CO2 diffuser membrane, check the regulator has not crept, and pull the deepest stems for a hard replant. Lights lose output long before they fail — plan on replacing LEDs or bulbs on a schedule, not on symptoms. |
Make it yours
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