The best siphons and gravel vacuums for goldfish

A goldfish water change is not a delicate operation. It is moving a lot of water and a lot of settled waste, once a week, for as long as you keep the fish.

Two specifications decide how that goes, and neither is on the front of the packet.

What to look for

The bore of the tube. Not the length. The width of the intake decides how fast the job goes, and — less obviously — how violently the thing pulls at your substrate. A 2-inch mouth passing the same volume as a 1-inch one is moving water at a quarter of the speed, and that difference is the whole of whether sand stays where it is.

Manufacturers size these by tank volume. For goldfish, which start at 75–100 litres for one fancy and climb steeply, the large sizes are the relevant ones: one fancy starts at 75 to 100 litres, a second adds 40 to 50, and a single-tail needs 150 to 200 before it needs a pond.

Whether you have to carry it. The second specification is not really a specification at all. A common reason a goldfish water change does not happen weekly is that it is tiring, and a common consequence is nitrate creeping up over months — which how often to change the water treats as the thing that quietly decides how long a goldfish lives.

Anything that makes a 200-litre change easier is doing more for the fish than any refinement of technique.

Sand changes what you are buying

This site recommends sand or a bare bottom rather than gravel, for reasons the substrate guide sets out — small gravel lodges in a goldfish’s mouth, and that is not a theoretical risk.

That has a consequence for this purchase that most vacuum marketing ignores, because most vacuums are sold for gravel.

On gravel, you push the tube in and the water is drawn up through the bed, carrying the debris with it. The gravel is too heavy to lift and falls back.

On sand, that would fill your bucket with sand. Instead you hover the mouth a centimetre or so above the surface, and the debris — which is much lighter than sand — lifts while the sand does not. The cleaning guide covers the technique.

Which makes the bore matter twice over: a wide mouth is not only faster, it is gentler, because the intake velocity at the sand surface is lower for the same flow. The narrow vacuums sold for small tropical tanks are precisely the wrong tool here.

The bucket is the real constraint

Work it out for your own tank before deciding this does not apply to you.

A 200-litre tank at a 30% weekly change is 60 litres out and 60 litres back. That is roughly six full buckets each way, twelve lifts of about 10 kg, every week. The volume calculator will give you your own number.

A water change, step by step

1. 1 Test first Nitrate tells you how much to change. Ammonia or nitrite above zero means change more, sooner.
2. 2 Siphon out 25⁠–⁠50% Vacuum the substrate as you go. Old water goes to the drain, never back in.
3. 3 Treat the new water Dechlorinator for the full volume you are adding. Use a conditioner labelled for chloramine; test for ammonia afterwards.
4. 4 Match the temperature Within a degree or two of the tank. A sudden temperature change stresses the fish.
5. 5 Refill slowly Pour onto a plate or decor so the substrate is not stirred and the fish are not blasted.

Nobody plans to skip a water change. What happens is that the weekly one drifts to ten days, then to a fortnight, and the nitrate baseline climbs a little each month until a test reads a number that seems to have come from nowhere.

A tap-connected system removes the lifting entirely: one hose from the tap to the tank, drain, then switch it to fill. For a large goldfish tank it is the single purchase most likely to change what actually happens week to week.

Two things a tap-connected system changes

Neither is a fault, and both catch people out.

The conditioner now has to cover the whole tank. Refilling from the tap puts untreated water directly into the aquarium, so the dose is calculated on the tank volume, not the volume you replaced, and it goes in before or during the fill rather than after. This is the same arithmetic the medications page insists on for everything else, and the source water guide covers why chloramine in particular needs treating rather than standing.

The temperature is set at the tap. With buckets you mix and check before anything reaches the fish. With a hose you are adjusting a mixer tap and trusting it, so run it to temperature before connecting, and refill slowly enough that the tank as a whole barely moves.

What it does not do

The category contains one product type that needs its limitation stated plainly, because the marketing does not.

A battery vacuum that returns the water to the tank has not changed any water. It lifts debris into a cartridge and puts the water back. The substrate looks clean and the nitrate has not moved, because nothing left the system.

For goldfish that distinction is not a technicality. Nitrate export is the main reason the weekly change exists — the filter converts ammonia to nitrate, and water changes are the main way it leaves the tank, though plants and denitrification remove some. A tool that tidies without exporting is a genuinely useful supplement and a harmful substitute, and the difference is invisible if you judge by how the tank looks.

When you do not need to buy one

A bare-bottom tank needs a hose, not a vacuum. Covered above.

A small interim or hospital tank is emptied faster with a jug. A hospital tank rarely justifies dragging out the full kit.

A pond is a different problem with different equipment, and a pond through the year covers the seasonal cleaning that actually matters out there.

And if you already have one that works, there is nothing here worth upgrading to on refinement alone. The only upgrade that changes outcomes is from buckets to no buckets.

How you know the tool is keeping up

The siphon is not the thing to judge. The nitrate is.

A water change regime is working if nitrate sits at a stable figure week after week rather than climbing month on month, and the only way to know which is happening is to write the number down. Testing goldfish water covers what to test and how often; the reading that matters for this purchase is the trend rather than any single result.

If nitrate is creeping despite a weekly change, the usual causes are in this order: the change is smaller than you think, the substrate is holding waste the vacuum is not reaching, or the tank is carrying more fish than the routine suits — and how many goldfish can I keep is the uncomfortable check on the third.

Long-term nitrate is the quiet variable behind a great deal of what why did my goldfish die has to work through after the fact, which is the real reason this unremarkable piece of plastic matters more than most of the equipment on this site.

Our picks explained

Aqueon Siphon Vacuum, Large: best overall

The unglamorous answer, and the right one for most goldfish tanks. The Large is a 16-inch tube with a bore of about 2 inches (check the listing for the exact figure), which is the width that makes a big tank quick and sand manageable. It is the size we would look at for aquariums of about 150 litres and up, which is where goldfish keeping begins.

It is self-priming, so there is no squeeze bulb to perish and no reason to put a hose in your mouth. It comes with about 6 ft of hose.

Against it: 6 ft means a bucket, and on a large tank that is the limitation that matters. The rigid tube is also long for a shallow tank.

Python No Spill Clean and Fill: best for large tanks

The purchase that changes behaviour rather than technique. It connects to a tap, uses the flow to pull water out of the tank, and then reverses to refill — no buckets, no lifting, one setup for the whole job. Sold in several lengths (this one is 25 ft), so check the length against the distance from the tap to the tank.

Against it, and these are real: it needs a threaded tap, which a good many kitchen mixer taps are not, so check yours before ordering. It uses running water to generate suction. And both the conditioner arithmetic and the temperature move to the tap, as above.

Eheim Quick Vac Pro: best between water changes

A battery vacuum that catches debris in a fine mesh cartridge and returns the water. Listed at about 24 inches assembled and submersible to roughly 3 ft (check the current model), with a reusable cartridge.

What it is genuinely good at is the five-minute job: a patch of waste behind an ornament on a Wednesday, lifted without setting up a hose and a bucket. Over sand it is gentle enough to work well.

Against it: it exports nothing, its suction is far weaker than gravity on a large tank, and its working depth is short for a deep goldfish aquarium. Buy it as a supplement with that clearly in mind.

What we would skip

Narrow vacuums sold for small tanks. They are not a cheaper version of the right tool; they are the wrong tool, slower on a big tank and harsher on sand.

Squeeze-bulb primers. The bulb is the part that perishes, and self-priming tubes make it unnecessary.

Anything that promises to clean the substrate without a water change. See above. The substrate is not the thing the water change is for.

And a second-hand one, if it came from a tank you cannot ask about. Hoses and tubes are cheap, they are porous enough to hold what was in the last tank, and buying second-hand makes the case for used equipment nearly everywhere else. This is one of the places where the saving is not worth the question.