How to Clean Aquarium Substrate: Gravel, Sand and Soil

Table of Contents

• Why Substrate Cleaning Matters
• Cleaning Gravel Substrate
• Cleaning Sand Substrate
• Cleaning Active Soil Substrate
• Cleaning Bare Bottom Tanks
• How Often Should You Clean?
• Tools You Need
• Common Mistakes to Avoid
• Frequently Asked Questions

Why Substrate Cleaning Matters

Your aquarium substrate is not just a decorative base — it is a living environment. Millions of beneficial bacteria colonise the spaces between gravel particles, within sand grains and throughout aquarium soil. These bacteria are a critical part of your biological filtration, converting toxic ammonia into less harmful nitrate.

However, substrate also accumulates waste. Fish faeces, uneaten food, decaying plant matter and other organic debris settle into and onto the substrate over time. Left unchecked, this decomposing waste releases ammonia, fuels algae growth and can create anaerobic pockets that produce toxic hydrogen sulphide gas.

The challenge is cleaning effectively without destroying the beneficial bacteria that live there. Different substrate types require fundamentally different cleaning approaches — what works for gravel can ruin sand, and what works for sand can destroy active soil. Understanding these differences is essential for any aquarium owner.

In Singapore, where our warm water temperatures (28-32 degrees Celsius) accelerate both decomposition and bacterial activity, maintaining clean substrate is particularly important. Waste breaks down faster in warm water, and the narrow margin between healthy and problematic conditions shrinks.

Cleaning Gravel Substrate

The Deep Vacuum Method

Gravel is the most straightforward substrate to clean. The spaces between gravel particles trap debris, but they are large enough to allow a siphon to penetrate and extract waste without removing the gravel itself.

Step-by-Step Process

1. Start your siphon — Use a gravel vacuum (a wide tube attached to flexible tubing). Submerge the wide end in the tank and start the siphon by either priming with water or using a squeeze-bulb starter.
2. Push into the gravel — Drive the vacuum tube straight down into the gravel until it reaches the bottom glass. You will see debris — brown mulm and waste particles — being pulled up through the tube.
3. Lift and move — Once the debris flow slows, lift the tube out of the gravel (the gravel falls back down while waste continues into the siphon) and move to the next section.
4. Work in sections — Clean roughly one-third to one-half of the substrate per water change session. This ensures you are not stripping all the beneficial bacteria at once.
5. Watch the water level — Gravel vacuuming removes water simultaneously. Monitor your bucket and stop when you have removed 25-40% of the tank’s water — your target water change volume.

Areas to Focus On

Concentrate on open areas where debris visibly accumulates — near feeding zones, around the base of decorations and in corners. Avoid vacuuming directly around plant roots in planted sections, as this can uproot stems and disturb root systems.

Cleaning Sand Substrate

The Hover Method

Sand requires a completely different technique. Unlike gravel, sand particles are too fine to allow a siphon to penetrate without sucking up the sand itself. Pushing a gravel vacuum into sand will remove your substrate along with the debris.

Step-by-Step Process

1. Start your siphon — Use the same gravel vacuum, but this time, hold the wide end just above the sand surface — roughly 5 to 10mm above it.
2. Hover and swirl — Gently wave the vacuum tube in small circles above the sand. The suction pulls debris off the surface without disturbing the sand beneath. If you see sand being pulled up, raise the tube slightly.
3. Disturb, then collect — For debris trapped in the top layer of sand, gently stir the sand with a chopstick or thin stick to release trapped waste into the water column, then immediately hover the siphon over that area to collect the suspended debris.
4. Target waste piles — Sand tends to display waste more visibly than gravel — brown patches and mulm piles sit on the surface rather than sinking in. Work through these visible spots methodically.

Malaysian Trumpet Snails: Your Sand-Cleaning Allies

Malaysian trumpet snails (MTS) are invaluable in sand-bottom tanks. They burrow through the sand, aerating it, consuming buried organic matter and preventing the anaerobic gas pockets that sand is prone to developing. Many experienced hobbyists in Singapore intentionally maintain an MTS population in their sand tanks for this exact purpose.

Cleaning Active Soil Substrate

The Golden Rule: Do Not Vacuum Active Soil

Active aquarium soils — ADA Amazonia, Tropica Aquarium Soil, Fluval Stratum and similar products — should not be vacuumed in the traditional sense. Here is why:

• Structure damage — Active soils are granular and relatively soft. Aggressive siphoning breaks down the granules into mud, destroying the soil’s structure and its ability to hold nutrients and support root growth.
• Nutrient disruption — These substrates store nutrients that plants access through their root systems. Vacuuming disturbs this nutrient layer and can release trapped organic compounds into the water column, causing parameter swings and algae blooms.
• Beneficial bacteria loss — Active soils harbour enormous bacterial colonies. Disturbing the soil destroys established bacterial communities, potentially triggering mini-cycles.
• Shortened lifespan — Active soils already have a limited useful life (typically one to two years). Aggressive cleaning accelerates their breakdown.

What to Do Instead

For active soil tanks, limit your cleaning to light surface debris removal:

1. Hover the siphon — Hold it well above the soil surface, collecting only visible debris floating or resting on top.
2. Use a turkey baster — For targeted debris removal around plants and hardscape, a turkey baster or pipette lets you blast debris off surfaces and then siphon the clouded water without touching the substrate.
3. Let the plants do the work — In a well-planted tank with active soil, the plants themselves consume the decomposing organic matter as it breaks down. The system is largely self-maintaining.
4. Rely on your clean-up crew — Shrimp, snails and bottom-dwelling fish handle surface debris efficiently in most planted tanks.

Cleaning Bare Bottom Tanks

Bare bottom tanks — those with no substrate at all — are the easiest to clean. All debris sits visibly on the glass bottom with nowhere to hide.

• Simply run your siphon along the bottom glass, collecting all visible waste.
• A gentle sweep from one end to the other ensures nothing is missed.
• The entire bottom can be cleaned in a single session without concern about disrupting bacteria or substrate structure.

Bare bottom setups are popular in breeding tanks, hospital tanks and high-bioload fish rooms in Singapore. They sacrifice aesthetics for ease of maintenance and superior hygiene control.

How Often Should You Clean?

These frequencies assume standard stocking levels and feeding amounts. Heavily stocked tanks or those with messy eaters (goldfish, large cichlids) may need more frequent attention. Lightly stocked planted tanks with active soil may go weeks between surface cleanings.

Tools You Need

Essential Equipment

• Gravel vacuum/siphon — The most important tool. Choose a size appropriate to your tank — a wide-bore vacuum for large tanks, a narrower one for nano setups. For a comprehensive look at options, see our guide to the best aquarium gravel vacuums.
• Bucket — Dedicated to aquarium use only. Never use a bucket that has held soap, detergent or household chemicals.
• Dechlorinator — Essential for treating replacement water. Singapore’s PUB tap water contains chloramine, which requires a dechlorinator that neutralises both chlorine and chloramine. Seachem Prime is the most widely used option among local hobbyists.

Helpful Extras

• Turkey baster or pipette — For precision debris removal in planted tanks without disturbing the substrate.
• Thin wooden stick or chopstick — Useful for loosening debris from sand surfaces before siphoning.
• Algae scraper — Clean the glass before vacuuming so that dislodged algae gets picked up during the substrate cleaning pass.

Common Mistakes to Avoid

Over-Cleaning the Entire Substrate

Vacuuming every square centimetre of substrate in a single session strips a significant portion of your beneficial bacteria colony. This can trigger a mini-cycle — an ammonia and nitrite spike that stresses fish. Always clean in sections, alternating areas between water changes.

Vacuuming Active Soil Like Gravel

This is one of the most common mistakes among hobbyists transitioning from gravel to planted tanks with active soil. The first deep vacuum turns the water into a brown, silty mess and releases stored nutrients, often triggering an algae bloom within days. Treat active soil gently — surface debris only.

Forgetting to Dechlorinate

After removing water during vacuuming, the replacement water must be treated. Untreated tap water from Singapore’s PUB supply contains chloramine, which is lethal to beneficial bacteria and harmful to fish at the concentrations present in our tap water. Add dechlorinator to the replacement water before it enters the tank, or dose the tank directly before refilling.

Cleaning Substrate and Filter on the Same Day

Both substrate and filter media house beneficial bacteria. Cleaning both simultaneously can remove too much of your bacterial colony, risking an ammonia spike. Space out substrate cleaning and filter maintenance by at least a week.

Using Soap or Detergent

Never use soap, detergent or household cleaning products on anything that contacts your aquarium water. Even trace residues are toxic to fish and can destroy biological filtration. Hot water and manual scrubbing are sufficient for cleaning equipment.

Frequently Asked Questions

Can I stir my sand to release trapped gas bubbles?

Yes, and you should — occasionally. Sand substrates can develop anaerobic pockets where hydrogen sulphide gas (recognisable by a rotten egg smell) accumulates. Gently stirring the sand with a stick releases these pockets safely. However, do this before a water change so that any released compounds are removed with the old water. Malaysian trumpet snails prevent this issue entirely by continuously aerating the sand as they burrow.

My gravel has turned black underneath — is this dangerous?

Black discolouration beneath gravel indicates anaerobic conditions where beneficial aerobic bacteria have been replaced by anaerobic bacteria that produce hydrogen sulphide. This is dangerous if disturbed suddenly, as a large release of hydrogen sulphide can harm fish. Stir the affected area gently and gradually during water changes, allowing the gas to dissipate in small amounts. Going forward, ensure regular vacuuming reaches the deeper layers of gravel to prevent recurrence.

Should I remove fish before cleaning the substrate?

For routine vacuuming, no. Fish may scatter briefly when the siphon enters the tank, but they are not harmed by the process. The exception is if you are doing a major deep clean of heavily soiled substrate — the disturbance can cloud the water significantly, and temporarily housing fish elsewhere for an hour may be advisable.

How do I clean substrate in a shrimp tank?

Very carefully. Cover the siphon intake with a mesh or pre-filter sponge to prevent sucking up baby shrimp. Work slowly, checking for shrimp before moving the vacuum to a new area. In Caridina tanks using active soil, follow the soil-cleaning guidelines above — minimal disturbance, surface debris removal only. Your shrimp colony is one of your best cleaning crews; they handle much of the surface debris on their own.

Maintain Your Tank With Confidence

Proper substrate maintenance is one of the simplest yet most impactful things you can do for your aquarium’s long-term health. If you are unsure about the best approach for your specific setup, or if your tank needs a professional deep clean, visit Gensou Aquascaping at 5 Everton Park, Singapore. With over 20 years of hands-on experience, we maintain tanks across the island and can help you establish a routine that keeps your aquarium thriving. Get in touch to learn more.