Substrate & Soil Depth Calculator.

One to two inches is enough for a fish-only tank, which keeps waste visible and easy to siphon. Planted tanks generally want two to three inches so root systems have room to establish and anchor. Going much beyond three inches in fine sand without root structure or burrowing livestock raises the risk of compacted anaerobic pockets.

A widely used rule of thumb is about one pound of gravel or sand per gallon of tank capacity for a one inch bed, rising to roughly 1.5 to 2 pounds per gallon for a planted depth of two to three inches. Rules of thumb ignore your tank's footprint though, so calculating from actual length, width, and target depth as this tool does is far more accurate.

Gravel is inert, cheap, and lets debris settle into it, making it easy to vacuum. Sand gives a natural look and suits burrowing species but compacts more readily. Aqua-soil is a nutrient-rich planted substrate that actively feeds roots and often lowers pH slightly; it is lighter per litre than sand or gravel and typically has a usable lifespan of a year or more before it needs supplementing.

Divide your required bed volume by the bag size you intend to buy. Aqua-soil is commonly sold in 9 litre bags while gravel and sand are often sold by weight in 5 pound or larger bags, so this calculator reports both. Buying slightly more than the estimate is sensible, since sloping the bed higher at the back consumes extra material.

Rinse gravel and sand thoroughly, as both carry fine dust that will cloud the water for days. Aqua-soil is the exception: most brands should not be rinsed because doing so washes away nutrients and breaks down the granules. Instead, add aqua-soil dry and fill the tank slowly onto a plate or bag to avoid disturbing it.

Yes, noticeably. A two inch bed in a standard 29 gallon tank can displace several gallons, and combined with hardscape this is a large part of why net water volume typically runs 10-15% below the rated capacity. Use the displaced volume shown here when working out medication doses and <a href="/calculators/stocking">stocking levels</a>.