Aquarium algae control schedule: three variables, three weeks

The annoying thing about algae is that it is rarely a cleaning failure. A tank that grows algae usually has one of three things out of balance: more light than the plants can use, more nutrients than they can take up, or surfaces that never get disturbed. Scrubbing removes the symptom for a week. A schedule changes the arithmetic, and that is the part worth writing down.

The short answer

Fifteen minutes a week, in this order: scrub glass and hardscape, siphon 25–30% while the loosened algae is still suspended, remove the worst leaves, squeeze the intake sponge, and write down nitrate, light hours and how much you fed. Keep the light on a timer for 6–8 hours. If algae is still winning after two consistent weeks, work down the three-week ladder — and do not start with a chemical.

Identify before you act

The type of algae tells you which variable is out of line, which is why “add algae remover” is not a plan. Take a photo on the same day each week: colour and texture are easier to compare in pictures than in memory.

Two of those are not really algae. Diatoms are a stage, and cyanobacteria is a bacterium that responds to flow and nitrate rather than to light alone. Treating either as “algae” is how people end up buying the wrong bottle twice.

The weekly fifteen minutes

1. Scrape the glass and hardscape before the water change, not after. The loosened algae then leaves with the water instead of settling back onto the plants.
2. Siphon 25–30% from the substrate, slowly enough that you see the mulm lift. This is the only step that removes the nutrients algae are built from.
3. Remove leaves that are more than half covered. A melting leaf feeds the next outbreak; the plant replaces it in a fortnight.
4. Squeeze the intake sponge in the removed water. Flow is the variable people forget, and a clogged intake turns a clean tank into a still one.
5. Write three numbers: nitrate before the change, hours of light, and roughly how much food went in. Three lines are enough to see which one moved first.

The three-week ladder

Change one variable at a time and give each change a week, because algae responds on the scale of days but plants respond on the scale of weeks. If you change light, feeding and flow on the same afternoon, you learn nothing and the plants sulk.

Light: hours, intensity and the sun you forgot

A continuous photoperiod of 6–8 hours suits most low-tech planted tanks. Siesta splits help some tanks and confuse others; pick one and keep it for a month before judging. If you have already cut the hours and algae still grows, lower the intensity or raise the light — a weak light at the wrong height grows algae on the glass and starves the carpet. And count the daylight the tank gets for free: a bright room is a second photoperiod nobody scheduled.

Nutrients: feed the plants, not the algae

In a planted tank, nitrate around 10–20 ppm and phosphate around 1–2 ppm feed plants without feeding an outbreak. Above that, the surplus belongs to whatever grows fastest, and that is never the plant you paid for. Overfeeding is the usual route: a pinch that vanishes in a big tank is a week of phosphate in a small one, and uneaten food breaks down into exactly what algae wants. The water change schedule is the other half of nutrient control, and the calculator sizes the change to the nitrate you actually have.

Flow and surface movement

Dead spots collect mulm, and mulm is a nutrient bank with a slow release. Aim the outflow so the surface ripples and no corner is still; a small powerhead is often more effective against brush algae than another bottle. Clean the impeller when the flow visibly drops — a filter running at half rate is a flow problem disguised as an algae problem.

Clean-up crew: the last ten per cent

• Nerite snails graze glass and hardscape and lay eggs that will not hatch in freshwater. Two or three are plenty in a small tank.
• Amano shrimp eat algae and detritus and are the least disruptive addition to a community tank. Add a group, not one.
• Otocinclus eat biofilm rather than algae wafers, and they starve quietly in a tank younger than three months — read the care guide before buying.
• Never buy a fish to fix a maintenance problem. If the schedule is wrong, the grazer will not keep up, and you have added a fish to the problem.

Why algaecides are the wrong first move

An algaecide kills algae, and dead algae becomes ammonia and consumes oxygen as it decays — in a small tank, overnight. It also does not touch cyanobacteria, which is a bacterium, and it can set back the plants you are trying to favour. Use it only when the cause is known and the tank is being watched daily; otherwise the money is better spent on a timer and a test kit.

The exception: a new tank

Diatoms in the first six to ten weeks are not a failure, they are a stage while silica and biofilm settle. Keep the routine, do not chase them with chemicals, and do not add a clean-up crew to a tank that has nothing for it to eat. The cycling guide explains why the tank is unstable in exactly this window.

What the log tells you after four weeks

Four weekly lines turn algae from a mystery into a trend: nitrate climbing while light hours stayed the same means feeding or stocking, glass clearing later each week means the photoperiod is too long, and algae returning in the same corner means flow. Trends make that visible without rereading a notebook, and a recurring reminder is what keeps the fifteen minutes from sliding to Sunday night.

When to accept some algae

A little green on the back glass and older leaves is a grazer’s pantry and a sign the tank is producing food. The goal is not zero; it is a tank where the glass stays clear for a week and the plants outgrow the algae. If you are scrubbing the front glass twice a week, the schedule needs a variable changed — the maintenance schedule is where that hour belongs, and the nano guide covers the small-volume version, where a day of extra light matters more.