How to Water Houseplants With Aquarium Water

Yes, definitely. I’d go as far as to say that aquarium water is superior to rain, distilled, filtered, and tap waters. There are pros and cons for each, but overall, aquarium water has the most going for it.

What are the benefits of watering your house plants with fish tank water?

1 – Convenience

This is a big one, especially if you have a lot of plants and a small house.

I collect rainwater to water my house plants, but it isn’t always convenient. The water is stored outside and for nine months of the year I need to bring it inside to come up to room temperature.

This is fine if I’m just watering a few plants (and I remember). But if all of my plants need watering, I need to find room to put about five watering cans worth of water. It’s a bit of a ballache.

But the aquarium is right there. FULL of water. My boyfriend is big into fish, so we actually have two aquariums (aquaria?).

Watering house plants with the aquarium water is convenient even if you only have a few plants. You can dip your jug into the tank and water the plant straight away, without having to worry about the temperature or chlorine.

2 – Aquarium water has built-in fertiliser

This is linked to convenience again, but it’s a gamechanger, ESPECIALLY if you really care about your plants growing big and healthy.

Fertilising plants can be a whole big thing, requiring calendars, and lolly sticks (read more about that here) and a whole lot of knowledge. If you get it wrong, you can damage or even kill your plants.

But aquarium water comes pre-fertilised! Amazing! And you don’t need to worry about root burn, or picking a NPK value or anything!

Fish poop is an awesome fertiliser.

3 – Aquarium water is the perfect temperature

Tap water is too cold, as is rain water, depending on where you live and the time of year.

Distilled or filtered water is either too cold or room temperature. But aquarium water is temperature controlled (unless you have a coldwater aquarium, in which case it’s room temperature).

Room temperature water is 100% fine, but warm water is awesome, especially in winter.

This ties back in with convenience, I suppose, but it’s a big deal. Winter is hard enough for tropical plants, without having their roots doused in icy water. Having a large tank of warm water ready to go can really help in those cold winter months.

4 – It’s less wasteful than throwing away the water

There seems little point in pouring perfectly good aquarium water down the drain, and then running the tap to water your plants.

This seems like an obvious point, but it’s important. Both the house plant and aquatics industries have the potential to negatively impact the environment, so we should consciously seek to minimise our impact.

Is there anything wrong with watering house plants with aquarium water?

If you have a tropical or cold water aquarium that’s well-maintained, I can’t see the downsides of using aquarium water.

Are there likely to be some impurities in there? Probably, but fish are sensitive creatures. Those water conditioners that are added to make tap water safe are really good.

There’s also the risk that you’ll get algae growing on the roots but in my experience (I have a monstera being kept in a pint glass of water) algae looks gross but doesn’t harm plants in small amounts.

It probably goes without saying that you can’t water your house plants with water from a marine tank (well you can, but all your plants will die incredibly quickly), but I’ll say it anyway.

If you have an aquarium you’ll probably know that, but just in case. I see a lot of people hoping to buy a clownfish (usually looked harassed as their kids scream ‘NEMO!!!’) only to be told that they need specialised care.

Don’t go down that route unless you like money pits. Tropical all the way.

Can you put house plants in a fish tank?

Yes, but it isn’t easy.

There are very few amphibious plants, by which I mean ones that can live totally submerged in water, and completely out of the water.

Some nefarious aquatic plant growers will try to pass off house plants as aquarium plants (dracaena crop up a lot) but it’ll rot after a while.

I do grow some plants in my aquarium, but only the roots go in the water. They grow incredibly well. Like, amazingly fast with massive leaves even in winter.

But you need to get them to stay up. The easiest way is use rock work to wedge the roots in. But even then, the plants can easily flop.

One option would be hang the plants from the ceiling above the tank. Suspend a curtain rail or something above the tank and let the roots dangle in the water.

Don’t let any of your house plant’s leaves sit in the water. Not only will this cause your plant to rot, but it could cause problems for your fish if there’s a bacterial bloom or something.

Can you root cuttings in an aquarium?

Yes, and it’s my favourite way of rooting cuttings in water.

I’m not the best at remembering to change out the water in my propagation vessels, and you don’t need to if you’re propagating in a fish tank. I mean, you need to change the tank water, but I’m assuming you were doing that anyway.

(I cheat, since my boyfriend does all of the tank maintenance).

Why do cuttings root so well in fish tanks?

• Fish tanks are well aerated

One of the reasons you need to keep on top of changing the water in your propagation jar is that the oxygen in the water depletes quickly. In aquariums, oxygen is constantly being added to the water, usually by an air stone.

• Fish tanks are filtered

So all the grime and bacteria and nasties are being are being removed by the filter.

The aeration and filtration will both reduce the chances of your cutting succumbing to root rot.

The biggest threat to cuttings that are being rooted in water is rot. It’s a race between roots emerging and the cutting rotting. Rooting cuttings in a fish tank can give you a bit of a head start.

• Fish tanks are humid

Especially if they have a lid on. In an ideal world, you’d only fill your tank up three quarters of the way so you’d have ample room for cuttings, but we settled for a lid that only goes across 3/4 of the tank, and the cuttings can poke out the back.

Increased humidity can really accelerate root growth. The other two things that can accelerate root growth are warmth and light. Which is great because…

• Fish tanks are warm

I think I’ve covered this enough.

and

• Fish tanks are well lit

If you’re an aquatic fanatic then you’ll probably have a fancy-ass aquarium light that is not only full spectrum (and therefore perfect for plant growth) BUT it’s set to a timer so the light is consistent.

For those of you that don’t have an aquarium, I still recommend aquarium lights as grow lights. I have a whole article about it here.

Can you water Calathea with fish tank water?

If you know anything about Calathea, you’ll know why I’ve singled them out. In short, they’re a pain in the bum when it comes to water temperature, quality, and frequency.

I do use aquarium water to water my Calathea, and I’ve not had issue with crispy tips or edges (that weren’t caused by spider mites, anyway).

I have plans to try growing a Calathea in the fish tank next year, because I’m interested to see how they fare. Technically, it should be a match made in heaven, but Calathea are notoriously contrary, so I’m not counting my chickens.

Can you use aquarium water with Leca/semi-hydroponics set ups?

I spent a large part of last summer reading up on converting house plants to Leca, and there’s…a lot of information.

Since it’s an investment for this website, I bought all the crap you’re meant to – ph up and down, the General Hydroponics stuff, and it worked well. But I can’t think that aquarium water wouldn’t work well.

I’ve not got enough experience to say that using aquarium water with Leca is just as good as the traditional chemicals, BUT I have a few cuttings in leca that have only being given aquarium water, and they’re doing well.

My Philodendron golden dragon in particular seems to like aquarium water.

Rhapidophora tetrasperma seems less keen (the roots are amazing, but no new growth yet), but you can’t please everyone.

Is it worth setting up an aquarium to water your house plants?

NO.

NO.

NO.

The reason that using aquarium water is so convenient for me is that I don’t have to do anything other than scoop out the water. My boyfriend even fills my bottom-watering tray.

It’s his hobby. I do nothing. I don’t even have to buy the dechlorinator.

Aquariums are hard to set up, expensive, and take a while to mature to the point that you can add fish and water your plants with the water.

The larger (and more expensive) the aquarium is, the better the water quality is, in general. Any bacteria is diluted in a larger volume of water, and issues like bacteria and algae blooms are far less fatal if there’s a large body of water to absorb the impact.

If you’re tempted to get a little tank and keep a couple of danios in it, purely for your plants, I really wouldn’t bother unless you’re really interested in fish. Small tanks are hard to keep stable, and you’ll end up poor and frustrated for a couple of pints of water.

Should you find yourself a partner that loves aquariums? Yes. Though be aware that it’s a hobby that’s noisy, expensive, and will expand to fill your house.

How to get aquarium-like water without having an aquarium

• Buy some dechlorinator and add it to your tap water.

I have no idea how water conditioner breaks down the nasties in tap water, but it really does. My boyfriend has tried every brand going, and settled on the Seachem Prime. It’s pricier than others but goes a long way.

• Add an airstone and pump to your propagation vessel

Having increased aeration can really speed up root formation, and they’re pretty cheap to buy. You’ll need a pump, tubing, and an airstone. You can buy packs that have everything you need in them.

One thing to note: air pumps are NEVER silent. Oh, they might be for a few weeks, but then they’ll buzz. As someone that’s lived with fish tanks in a small house for 15 years, trust me, you’ll get used to it.

• Add a heatmat

We have one for our terrarium, and they work well. I would only use one for plants for the couple of months of the year when it’s super cold, but if you like propagating year-round, it might be a good investement.

• Ask for waste water at your aquatics store

I mean, they’re just going to pour it away anyway – you might as well ask! Just make sure they don’t put marine water in it!

A few notes on my fish tanks

Just in case anyone’s interested.

• We use tap water

A lot of people use RO (reverse osmosis) water, but personally, I think it’s too expensive and a wasteful process. It’s essentially a fancy way of purifying the water. I believe it’s more commonly used in marine tanks.

The tap water is treated with Seachem Prime water conditioner.

• We have a big tank, little fish, and a big-ass filter

So impurities are kept to a minimum. Fish poop is also present in much lower quantities than if we had a big predator like an Oscar (big fish = big poop, whereas little fish don’t have so much of an impact).

• We feed frozen food

I don’t know if this makes a difference but I THINK it means less waste. This will depend on how much you feed and how greedy your fish are.

• The lighting is fancy

Like, fancier than the Fluval COBs that I got when Dave replaced them. And those COBs are life changing (if getting growth on plants in winter changes your life – it did mine (a bit).

(I asked and it’s the Kessil A160WE Tuna Sun LED aquarium light. For that price it’d better root my cuttings overnight).

Cheaper lights may be less effective, though there are some awesome cheap aquarium lights out there. You can get them will all kinds of cool effects designed to bring out the colour of the fish and replicate the natural habitat.

• We have tannins in the water

Again, I have no idea if my plants like/don’t like this. Dave makes up roobios tea and adds it to the tank (obvs he cools it down). There will be tannins in the leaf litter in many house plant’s natural habitat, so I’m sure some of them will appreciate the tannins.

I hope this was helpful and answered some of your house plant/aquarium questions. Feel free to put any questions in the comments. I can field any fishy queries to Dave.