Choosing Substrate for Planted vs Reef Tanks

Substrate gets picked last and regretted first. Someone spends three weeks agonising over a filter, then grabs whatever bag of gravel is nearest the checkout, and six months later they're fighting algae or a pH that won't sit still. Planted tanks and reef tanks want almost opposite things from the stuff on the floor of the aquarium, and understanding why will save you a full teardown later.

Table of Contents

• Planted tank substrate basics
• Reef tank substrate options
• Comparison table
• Good, Better, Best picks
• FAQ

Planted tank substrate basics

Freshwater plants feed through their roots as much as the water column, so substrate in a planted tank is part filter media, part fertiliser bank. This is where ADA Aqua Soil earns its reputation. It's a fired volcanic soil that slowly releases ammonium and trace minerals, softens water slightly, and drops pH into the 6.0 to 6.8 range that carpeting plants like Hemianthus callitrichoides and Monte Carlo actually thrive in.

ADA aquasoil vs sand for planted setups

Plain sand looks tidy but it's inert. Nothing to buffer, nothing to feed roots, and it compacts over time, which starves anaerobic zones of oxygen and can turn sour. Aquasoil, by contrast, is porous and light, which lets roots push through easily and keeps beneficial bacteria colonised right where plants need them. The tradeoff is that aquasoil breaks down over two to three years and needs topping up or replacing, while sand is basically permanent. For a low-tech tank with hardy stems and swords, a sand and root tab combination from our freshwater substrate range can work fine. For a serious carpet or a competition-style scape, aquasoil is not really optional.

Depth and grain size for planted tanks

Aim for 4 to 6cm at the front sloping to 8 to 10cm at the back for a natural gradient. Grain size matters more than people expect. Fine grain aquasoil (roughly 3 to 5mm) suits carpet plants and small root systems. Larger grain versions handle bigger stem plants and are more forgiving if you like to replant frequently, since the soil doesn't turn to mud under your fingers.

Reef tank substrate options

Reef substrate does a different job entirely. It's not feeding anything, it's buffering calcium and carbonate hardness, hosting denitrifying bacteria, and giving fish like wrasses and gobies somewhere to sift and burrow. The two main options are dry aragonite and live sand.

Aragonite vs live sand

Dry aragonite is calcium carbonate, usually crushed coral or oolite, sold clean and inert until it's seeded by your live rock and cycling bacteria. It's cheaper, has zero risk of introducing pests, and lets you control exactly how much you add. Live sand comes pre-inoculated with bacteria and sometimes copepods, which can shortcut your cycle by a week or two, but it costs more and occasionally brings in unwanted hitchhikers like aiptasia eggs.

Grain size for reef tanks usually runs 1 to 2mm (sugar size) for a fine sandbed that sifting fish enjoy, or 2 to 4mm for a slightly coarser bed that resists getting blown around by strong flow from gear like the Vortech QuietDrive. Bare bottom tanks skip substrate altogether for easier detritus removal, which is common in SPS-dominant systems where flow is aggressive and any loose sand ends up in a dune against the overflow.

Substrate depth in reef tanks

Deep sand beds of 7 to 10cm can support denitrification but need careful management to avoid nutrient dumps if disturbed. Most home reefers in Brisbane run a shallow bed of 2 to 3cm, mostly for aesthetics and fish behaviour, and lean on protein skimmers and refugiums for nutrient control instead. If you're chasing a deep sand bed, go in knowing it's a long-term commitment, not something you stir up on a whim during a big water change.

Planted vs reef substrate comparison

Good, Better, Best substrate picks

Good: plain river sand with root tabs from the freshwater substrate range for a beginner low-tech planted tank, or dry aragonite alone for a simple fish-only-with-live-rock marine setup. It works, and plenty of long-running tanks are built on exactly this, but you'll be dosing more liquid fertiliser or watching alkalinity more closely to make up for what the substrate isn't doing.

Better: a proper aquasoil base under a fine cap layer for planted tanks, giving you the nutrient release without the muddy look aquasoil alone can have when disturbed. For reef tanks, a mix of live sand seeded over dry aragonite gets you biological activity without paying full price for live sand across the whole bed. We've seen this combo cycle noticeably faster than dry aragonite alone.

Best: full-depth ADA Aqua Soil (Amazonia or Africana depending on your water hardness) paired with root tabs from our plant food range for a planted tank that needs almost no dosing adjustment for the first year. For reef, a shallow sugar-sand bed of quality live sand plus strong, well-placed flow from something like the Vortech QuietDrive to stop detritus settling into the sand and causing localised nutrient spikes. It costs more upfront, but you're not fighting the substrate later, which is the whole point.

FAQ

Can I mix ADA aquasoil with regular sand?

Yes, capping aquasoil with a thin layer of fine sand is common for aesthetics, but keep the cap under 1cm or you'll blunt the nutrient exchange the aquasoil is there for.

Do reef tanks need substrate at all?

No. Bare bottom tanks are standard in high-flow SPS systems for easier cleaning. Substrate is more about fish behaviour and appearance than a biological necessity, since live rock does most of the filtration work.

How often does aquasoil need replacing?

Most aquasoils lose their nutrient charge and start compacting after 2 to 3 years. At that point plants usually tell you first, growth slows and older leaves yellow even with dosing.

Will aragonite raise my reef tank's pH too much?

No, aragonite buffers toward stable seawater pH (around 8.1 to 8.4), which is exactly the range reef inhabitants need. It's a stabiliser, not a spike.

Still deciding between soil types or sand grades for your tank size? Browse our aquascaping tools or drop into the Brisbane store and we'll talk through what your specific stock list actually needs.

Prices are accurate at the time of publishing and are subject to change. Check the product page for the current price before buying.