What an Aquarium Costs Per Year to Run: About $45 of Refills

October 10, 2026

Ask what an aquarium costs and you’ll get a setup list. Tank, stand, filter, heater, light, substrate, and a total somewhere between three hundred and a thousand dollars depending on how honest the person is being about the stand.

Then the answer stops. Which is strange, because the setup is the part you pay once.

I’ve been running the same 40-gallon planted tank for years now, deliberately built so it needs as little from me as possible. The hardware bill was settled a long time ago. What I actually spend money on is a short list of bottles and pads that run out on a schedule — and nobody prices that list, so I sat down and did it.

The short version: about $45 a year. Under four bucks a month. And a decent chunk of that is stuff I’d tell you to skip.

Why the setup number is the less useful half

A setup cost is a one-time decision you make with a lot of research behind it. You read for a week, you buy, you’re done.

Consumables are different. They’re a dozen small decisions you make while tired, usually in a cart at 11pm, usually at whatever size the store put in front of you. That’s where the waste is. Nobody overspends by $400 on a filter — they overspend by $15 a pop, six times a year, buying the big bottle because the per-ounce math said to.

And for a tank designed to be left alone, the recurring list is where the whole idea either proves itself or doesn’t. A tank that needs constant correction eats reagents, conditioner and media. One that’s stable mostly sits there growing plants. The receipts should show that difference. Mine do.

The reorder table

Here’s my actual year, with the working shown. The tank is 40 gallons, low light, modestly stocked, one 25% water change a month and a top-off of about a gallon a week. That’s 172 gallons of replacement water a year, which is the figure most of the dosing hangs off.

Two things jump out of that table.

The first is that food is the biggest line, by a distance. It’s the one consumable that scales with how many fish you keep rather than how much water you have, and it’s the one nobody thinks of as a running cost. The second is that the three items people associate most strongly with “aquarium upkeep” — conditioner, test kit, filter media — come to about fifteen dollars between them.

Reagents expire whether you use them or not

This is the line item I got wrong for years.

Test reagents are not equipment. They’re chemistry with a date on it, and they degrade sitting in a cupboard. Hach — who make the water-analysis reagents that municipal labs run on — put it in their warranty in plain language: the warranty “does not apply to consumable products such as chemical reagents.” Not a product. A supply.

So the capacity number on the box is a trap for a tank like mine. The API master kit is rated for 800 tests. I test this tank monthly. That’s sixty-six years of testing, in a box that will be chemically useless long before the dropper bottles are empty, and the expiry on it ticks down at the same rate whether I test weekly or never.

You can see where the money goes. I don’t pay for tests. I pay for a kit to sit still and get old.

I’ll be straight about the limits of what I can tell you here: I went looking for a published shelf life on the hobby kits and couldn’t find one from the manufacturer that I’d stand behind. The figures that circulate online all trace back to forum posts quoting each other. So — read the date printed on your own bottles, and don’t let me or anyone else give you a number we can’t source.

The practical fix is smaller packages, more often. Strips for routine checks, and a liquid kit bought fresh when you have an actual problem to diagnose.

What a low-intervention design takes off the list

A few things are missing from my table that sit on most people’s, and the absences are the real argument for building the tank this way.

Filter cartridges. Gone entirely. The coarse sponge rinses out in old tank water and goes back in; Co-Op says it’ll last years of normal use and mine has. Cartridges are the alternative, and they get swapped monthly by people following the box instructions — Co-Op’s own listing for the sponge calls them costly and positions the pad as the replacement. I’d put it harder than that. A part whose main function is to throw out your bacteria colony twelve times a year is one you’re paying to work against yourself.

Bacteria starter. You need it once, when you cycle. After that a stable tank is making its own.

Algae treatments and clarifiers. If you’re buying these on a schedule, the schedule is the symptom. Read what the algae is telling you and fix the light or the feeding instead.

Most of the water-change volume. A bigger, understocked, over-filtered tank genuinely needs less swapping out, which is less conditioner and less of your Saturday. I’ve written up why a bigger tank is less work and how long a tank can actually go between changes.

Add it up and the design doesn’t just save you time. It removes line items.

The two things people rebuy monthly and shouldn’t

Water conditioner, in the big bottle. Dechlorinator is enormously concentrated — a millilitre per ten gallons — and a monthly-water-change tank sips it. My 172 gallons a year is seventeen millilitres. Seventeen. The 16 oz bottle holds 473 ml, so I’d be on that bottle until roughly 2053. Buy the little one. It feels wrong at the till and it’s right.

Filter media, on a calendar. Media gets replaced when it stops flowing, not when a month rolls over. The coarse sponge and the bio media are effectively permanent; only the fine polishing layer is a genuine consumable, and even then one $8.99 sheet cuts into enough pieces to cover a year. If you want the detail on which layer does what, I worked through it in the filter media stack that goes months between rinses.

So what’s the honest number?

For a mid-size, low-light, modestly stocked planted tank that’s been left to settle: $40 to $75 a year.

The spread is almost entirely stocking and light. Add fish and the food line climbs fast. Run medium light instead of low and the fertiliser dose doubles, which adds about ten dollars. Keep something that needs close watching and the testing line goes up, fairly.

What it won’t do is creep past a hundred dollars without you deciding it should. Which means the real cost-of-ownership answer for this hobby isn’t the tank — it’s that the second year costs less than one decent dinner out, as long as you stop buying the big bottle.

Price the refills before you buy the tank. It’s the half of the answer that tells you whether you can live with the thing.