Aquarium Maintenance: Weekly and Monthly Tasks

An established planted tank needs remarkably little attention, but it needs it consistently. The failure mode is not neglect that kills fish overnight — it is a routine that slips, a nitrate trend nobody noticed, and a crash three months later that seems to come from nowhere.

The weekly forty minutes

Test nitrate

Before anything else, so the number reflects the week just finished rather than the water change about to happen.

Unplug the filter and heater

Always. The filter intake can trap a hand, and a heater left on while the water level drops will crack.

Remove dead leaves and debris

Every yellowing leaf is an ammonia source. Net out floating fragments before they root in the filter intake.

Change 25–30% of the water

Vacuum the substrate surface as it drains. Hover over sand rather than pushing the tube into it.

Clean the glass

Blade for green spot, pad for soft film. Rinse the blade after every stroke on a sandy tank.

Trim what has outgrown its space

Anything reaching the surface, and any carpet that has thickened enough to shade its own base.

Refill at matched temperature

Dechlorinator dosed for the full tank volume, added before the new water. Within 1–2 °C of tank temperature.

Plug everything back in

And confirm the filter is actually running. A filter left unplugged overnight loses a measurable part of its colony.

Never change more than 50% at onceA large change swings temperature, pH and hardness simultaneously. Livestock can tolerate a 30% change every week indefinitely; a 70% change can kill a tank in an afternoon.

The monthly twenty minutes

Service one filter tray

One, not all. Cleaning the whole stack at once removes the entire bacterial colony and resets the cycle. Rotate through the trays month by month.

Rinse media in tank water

Use the water you just drained. It is tank-temperature and dechlorinated, which is exactly what the bacteria need. Never a tap.

Check the impeller

Remove it, clear any debris, and check for wear. A sudden flow drop is nearly always a clogged impeller or a kinked hose, not a failed motor.

Test GH and KH

Especially if you run aqua soil or inject CO₂, both of which deplete KH.

Inspect the heater and the cables

Look for cracked seals, brittle insulation and any cable that has been sitting in water. Check that every cable leaving the tank has a drip loop.

Refresh root tabs under heavy feeders

Every 8–12 weeks in an inert substrate. Aqua soil holds nutrients longer, but even it exhausts after 12–24 months.

The quarterly and annual jobs

Quarterly: check CO₂ tubing and fittings for hardening or leaks. Replace the check valve on any air line. Clean the diffuser by soaking it in a dilute bleach solution and rinsing for ten minutes.
Quarterly: inspect hardscape stability. If any stone can be moved with a net, it is a hazard to livestock and to the glass.
Annually: replace the CO₂ cylinder before it empties rather than after. Running out mid-week drops CO₂ to zero and stalls the plants.
Annually: assess substrate. Aqua soil that has been in place for two years is no longer supplying nutrients, and the choice is root feeding or a rebuild.

Media rinsed in drained tank water. The distinction between tank water and tap water is the whole difference between a filter service and a cycle crash.

Why consistency beats intensity

A 30% change every week keeps nitrate at a predictable equilibrium. A 60% change every three weeks does not — it lets nitrate climb to a peak and then halves it, so the tank swings between two states instead of sitting in one. Fish, shrimp and plants all do better in stable conditions, and stability comes from frequency, not volume.

Make the routine easy enough to actually doThe commonest cause of a tank going wrong is a water-change routine that is physically annoying. A hose system that drains and refills without buckets, a dechlorinator bottle kept beside the tank, and a tape mark on the glass for the target level turn a forty-minute chore into a fifteen-minute habit.

The warning signs, and what they mean

Aquarium Maintenance: Weekly and Monthly Tasks — data
Symptom	Likely cause	First action
Fish gasping at the surface	Low oxygen or CO₂ overdose	Switch CO₂ off, increase surface agitation
Sudden cloudy water	Ammonia spike, bacterial bloom	Test ammonia, water change, stop feeding
Nitrate climbing over three weeks	Bioload outgrew the routine	Larger or more frequent changes
Plants stalling, algae growing	CO₂ or flow limitation	Check flow distribution before dosing
pH will not hold steady	Depleted KH	Test KH, restore buffer
Shrimp dying at moult	GH too low or too high	Test GH, adjust gradually
Filter flow dropping	Clogged impeller or media	Service the impeller, rinse one tray

None of these require specialist knowledge to resolve, and all of them are much easier to resolve when caught in the first week. The routine exists to catch them in the first week.