Why Use a Gravel Calculator for Your Aquarium
Gravel sets the stage for everything that happens inside the aquarium. Plants anchor in it, helpful bacteria grow on it, and fish interact with it all day. If the layer is too thin, roots float free and plants weaken. If it is too thick, pockets of stale water can build up and upset the balance. Guessing the gravel needed for your aquarium leads to one of those extremes and disturbs the vibe of the whole tank.
A gravel calculator ends the guesswork. Just enter the tank’s length, width, and the depth of the gravel bed you want. The tool returns the exact amount of substrate in kilograms, pounds, or litres, taking the density of your chosen material into account.
Quick-Start Guide to the Calculator
- Type the length, width, and desired gravel depth in whichever unit you want.
- Pick the unit you prefer for the result.
- Adjust the depth slider to preview different scapes before a single pebble lands in the tank.
Recommended Gravel Depths
| Tank Size | Planted Setup | Fish-Only Setup | Shrimp & Nano Tanks |
|---|---|---|---|
| Under 40 L (10 US gal) | 4–5 cm | 3 cm | 2–3 cm |
| 40–120 L (10–30 gal) | 5–6 cm | 3.5 cm | 3 cm |
| 120–250 L (30–65 gal) | 6–7 cm | 4 cm | 3–4 cm |
| 250 L + | 7–8 cm | 4–5 cm | 4 cm |
Choosing the Right Gravel
Gravel shapes water chemistry, anchors roots, and sets the tone for the entire aquascape. Before buying a single bag, think about grain size, hardness, and colour. Mid-size grains (two to four millimetres) usually suit most community tanks because they let water flow yet keep waste from sinking too deep.
Quartz or Silica Stone
Quartz stays chemically neutral, so it will not alter pH or hardness. Community tanks with tetras, barbs, or guppies benefit from this stability. A light surface also bounces extra light toward low-growing plants.
Clay-Based Plant Soil
Fired clay pellets act like nutrient sponges. Stem plants send roots through this medium quickly and show stronger colours. Give the pellets a brief rinse first; otherwise a dusty haze can cloud the water.
Polished River Pebbles
Smooth edges protect bottom dwellers such as corydoras and loaches. The extra weight pins down wood and rock, preventing hardscape shifts when fish dig or when water currents pick up. Pair with a thinner under-layer or mix in finer grains so debris cannot slip through wide gaps.
Crushed Coral or Aragonite
Ground coral slowly dissolves, raising carbonate hardness and keeping pH steady—ideal for African cichlids or many marine setups. Soft-water species like discus or wild bettas prefer something gentler, so avoid coral if the goal is low mineral content.
Dark Lava Rock
Porous and lightweight, lava offers enormous surface area for beneficial bacteria. Its deep colour hides algae films and makes bright fish colours pop. Rinse thoroughly to remove black dust before filling the tank.
Match the shade of the gravel to the scene you want. Dark beds highlight neon fish, while pale sand sets off lush, green stems. Always choose products labelled “aquarium safe” and steer clear of painted pebbles that may shed toxic flakes over time.
Density Cheat Sheet
| Gravel Type | Approx. Bulk Density (kg/m³) |
|---|---|
| Quartz or River Gravel | ≈ 1 500 |
| Clay-Based Plant Substrate | ≈ 1 200 |
| Crushed Coral / Aragonite | ≈ 1 400 |
| Fine Sand | ≈ 1 600 |
Figures represent loosely poured, rinsed substrate. Compaction, moisture, and grain shape can shift the actual density by ± 5 %. Always check the manufacturer’s label if an exact value is provided; enter that number in the calculator for the most accurate result.
Pro Tips for Layout Success
- Create a front-to-back slope. Start shallow at the front glass, then add more substrate toward the rear. The gradient gives plants extra root depth, hides equipment bases, and adds depth to the scene.
- Lock slopes in place with structure. Low retaining walls of lava rock, wood, or plastic mesh keep gravel from sliding forward during water changes or playful digging.
- Rinse thoroughly before the first pour. A quick bucket wash removes dust that would cloud the water and clog filter pads.
- Cap nutrient soils with plain gravel. A one-centimetre cover of inert quartz prevents clay or aqua soil from floating while letting roots reach nutrients.
- Plant with long tweezers. Tools slip stems into place without disturbing the bed, reducing murk and protecting delicate tips.
- Vacuum in short, gentle passes. Hover the siphon just above the surface to lift debris while leaving beneficial bacteria on the grain.
Frequently Asked Questions
How much gravel do I really need?
Start with one pound per US gallon if you aim for a modest three-centimetre bed. Use the calculator for an exact figure once you know tank length, width, and target depth to avoid buying spare bags that never leave the closet.
Will coloured gravel harm my fish?
Quality products seal pigment inside an epoxy coating, so they stay inert and safe. Rinse until the water runs clear, then test a small scoop in a separate container. Flaking or cloudy runoff signals a poor-grade product, so its better to return it than risk livestock.
Can I mix sand and gravel?
Yes, but layers shift over time. Fine sand sinks beneath larger stones and can create oxygen-starved pockets. Keep each layer shallow or separate them with plastic mesh to maintain some circulation.
Does gravel change water chemistry?
Quartz, polished river stone, and baked clay remain neutral. Crushed coral, marble chips, and limestone raise pH and hardness—ideal for African cichlids but stressful for soft-water species such as discus. Match substrate to livestock needs.
How often should I vacuum the substrate?
Give the surface a light skim at every weekly water change. A deeper stir is needed only in open areas without rooted plants, roughly once a month. Avoid tugging at planted zones, as roots and bacteria do the needful there.
Is it safe to reuse old gravel?
Yes, provided it is free from soap, bleach, or copper residue. Rinse well, spread it on a tray, and let it dry completely in sunlight. Discard any pieces that smell foul or feel slimy even after washing.
What if I want to change gravel depth later?
Remove décor, scoop excess into a clean bucket, or add rinsed gravel in stages no deeper than two centimetres at a time. This preserves beneficial bacteria and prevents sudden ammonia or nitrite spikes.
Do I need to rinse new gravel every time?
Always rinse, even if the bag claims to be “pre-washed.” Dust from transport settles inside and will cloud the tank. A colander under running water or several bucket swirls clears fines in five minutes.