How do I safely change the water in a small aquarium?
December 10, 2014 5:59 AM   Subscribe

Aquarium pros, please help me change the water in my kid's fish tank for the first time.

A couple of months ago, beloved daughter won four "free" fish (grumble grumble $60 worth of tank and supplies for four "free" 99 cent fish) at a school fundraiser. Today, it's evident that John, Paul, George and Ringo need to get their tank freshened. I've never done this before, and I'm petrified that one or more of the little guys won't survive if I do something wrong.

So, in layman's terms, how do I do this, step-by-step? Are there any tips you can share, things you've learned over the years that make the process goof-proof? Do all of the rocks and the yellow submarine and all that need to be rinsed, or do we buy special chemicals, do we do something to the water first, etc.? Do I need to do something to the new water before putting them back in? Talk me through this, please, because my girl will be devastated if something goes wrong.
posted by jbickers to Home & Garden (21 answers total) 8 users marked this as a favorite
Okay, here is my guide to dealing with stupid fish (it's long, I apologise):

First off, don't change all the water. There's good bacteria and other microorganisms in the water, helping to keep your fish healthy, and completely replacing it could be as harmful as not replacing it at all.

Secondly, yes, you need chemicals for the water. Tap water is not fish safe - there's plenty of chlorine and the like in it, so you need a water treatment chemical. Head to your pet store, and pick up one that just says it treats water. You can also pick up another chemical that is supposed to calm down the fish. I can't remember the brand names, but we pick up stuff called Tap Safe and Stress Coat. Tap Safe cleans the water, Stress Coat makes the water change less harmful to the fish.

So now you're ready for the water change.

Start off by taking out a bit less than half the tank's capacity. Take the decor out as well. The fish might freak out a little while you're doing it, but they'll be okay afterwards, because they're still in the same water and it feels like home to them.

If there are pads in the filter, take those out as well. To make it easier on you, pop everything in the same bucket with the dirty water and carry it over to the tap.

Pour out the dirty water (and if you have a garden, this is the best time to water it - all that fish crap makes for excellent fertiliser). Rinse the filter pads under the tap, and if the decor is covered in gunk, give it a quick scrub with an old toothbrush or something similar. Nothing has to be spotless, just less dirty.

Fill up the bucket to about the same amount as the water you dumped. Add the Tap Safe according to the ratios listed on the label. Add a few drops of Stress Coat as well if you bought it. Make sure the water isn't too cold or too hot - you would hate it if someone dumped ice water in your bathtub, and they're tinier and more prone to shock.

Give it a few stirs and a bit of a wait to get the chemicals all through. Then slowly pour it back into the tank. I like to pour it from high, because the waterfall effect helps churn up the water and aerates it a bit more.

Put the pads back in the filter and the decor back into place. Wait for the fish to calm down, then give them a tiny bit of food as a treat.

And there you go. You have successfully changed the water.

Now do it all again in a month's time. And repeat.

Okay, and here's where we have to think about the future.

I'm guessing these are goldfish? Because goldfish are notorious for making their tanks filthy. They're just eating and shitting machines of golden delight. So I know you bought a tank, but if you're going to keep them around, you're going to need a bigger tank. You're always going to need a bigger tank. I mean, hell, this motherfucker wants a bigger tank, and the only way I can get bigger is if I convert the entire dining room into his personal underwater palace.

A bigger tank means they have more room to move around, and more time between "ahhh, nice clean water...for me to poop in!" and "oh god too much poop *choke* *dead*". It's a pain in the ass, but if you want to keep these little bastards alive, it's what you have to do. Plus, bigger tanks have built-in filter systems, which help keep the water clean and stop everything from becoming a disaster zone.

And don't overfeed them. Things get so gunky so quickly when the fish are overfed. It's not just the sheer amounts of crap they produce, it's the food they don't eat gunking up the system as well. You're only supposed to feed them as much as they eat in a minute. And it doesn't matter how desperate they look - they're conniving little bastards and always look hungry.

You'll be fine. The Fab Four will be fine. And if you have further stupid goldfish questions, feel free to ask me. That dumbass up there's been alive for over 12 years, and that involved two cross-town moves and four tank upsizes.
posted by Katemonkey at 6:30 AM on December 10, 2014 [16 favorites]

Buy one of these, and some of this, and two buckets, one for clean water ONLY, one for dirty water. Use the vacuum to suck out half the tank of dirty water and replace it with clean water, adding as much water conditioner as needed as per the label. Perform future 25% water changes every week, unless you've got a truly rockin' filtration system.

No offense intended, but... months for a water change? This is a living creature, same as any other pet. Asking it to sit around in its own urine for ages and ages is not particularly great ownership (I know you didn't want them, but you've got them now.)
posted by Nyx at 6:33 AM on December 10, 2014 [1 favorite]

I use two buckets for water changes, and usually fill and treat the "clean water" bucket (actualy a giant pitcher) a couple hours earlier, just to be sure the water is room temp when I go to add it. And I usually change about 20% of the water every week or two.
posted by the christopher hundreds at 6:41 AM on December 10, 2014

If you do have a filter, DO NOT run the filter cartridge or sponge under tap water! That could kill off all the good bacteria you have going in your nitrogen cycle. Fill a bucket with some of the water you already have in your aquarium and swish it through that water if your cartridge or sponge needs it.

What size tank do you have? What species of fish? I'm assuming goldfish. They're big waste-producers and definitely need filtration. I can give you really specific step-by-step instructions on tank care if I know the size of aquarium you're working with.
posted by BreannaBear at 7:00 AM on December 10, 2014

You can help out the filter by, when you have taken water out of the tank, using a turkey baster to get in the pebbles at the bottom and suck out a bunch of the fish crap manually. I have a 5-gallon tank, so not really big enough to justify a vacuum, and the turkey baster helps a lot.
posted by fiercecupcake at 7:01 AM on December 10, 2014

One trick-- you can remove water pretty easily by making a small hole in the top of a two-liter bottle. Push the bottle in the water neck-down. When it's as full as you can get it, put your finger firmly over the hole, lift the bottle straight out of the water, transfer to bucket. The vacuum will keep the water in the bottle well enough to transfer without a lot of maneuvering.

I thought of that myself!
posted by Mayor Curley at 7:02 AM on December 10, 2014 [2 favorites]

1) Using a siphon or a hose or even a coffee cup or a tupperware container scoop out approximately 25% of the water in the tank. Eventually you will want to get a siphon that lets you vacuum the gravel such as this one.

2) Fill an empty gallon water jug or a CLEAN (never used for mopping) bucket or a clean juice pitcher with water that is approximately the same temperature as the water in the tank.

3) Add Tap Safe or whatever chemical your bought per the instructions on the jar. I, personally, like Seachem Prime. If you don't have any chemicals right now, you can either let the water sit out for 24 hours or buy bottled (distilled) water until you get to the pet store.

4) Slowly pour the water into tank.

5) Repeat steps 2-4 until the tank is back to 100% full.

Do this every 2-4 weeks.
posted by LittleMy at 7:07 AM on December 10, 2014 [2 favorites]

Agreed with Breanna, we'll be able to help you more if you can tell us exactly what kind of fish you have and in what size tank.

I strongly recommend reading up on the nitrogen cycle, to understand the interaction between fish waste, friendly bacteria colonies in you filter and gravel, and the need for water changes. (As you might have guessed from people's responses, aquaria need water changes long before grime becomes visible to the human eye.)

Then, purchase a water testing kit and learn how to use it. Get one which uses drops, not strips of paper -- drops are more accurate and you'll save money in the long term. Although it's a good idea to change your tank's water on a regular schedule no matter what, it's important to know exactly what's going on with your water when you need to.

Lastly, involve your daughter as much as possible in the fish care process. Not only will she learn a lot about biology and ecology, but the lesson that even "easy" pets require a fair amount of research and care is a valuable one that she'll carry well into adulthood. And hey, if your fish are goldfish, she might be carrying those into adulthood too. Properly cared for, they can live for decades.

Thank you for trying to be a good fishkeeper, and not just dumping them into bowls!
posted by bettafish at 7:15 AM on December 10, 2014 [2 favorites]

Response by poster: Thanks for all the input so far, folks. They are indeed goldfish (tiny right now, but I'm shocked to learn how big they can eventually get!), in a very small tank (3-4 gallons, maybe? I'm at work right now so not totally sure). It does have a filter and a light in the topper, it's not just a bowl. The guy at the pet store instructed my daughter to run the filter about 6-8 hours a day, and to feed sparingly. (Daughter is very involved, BTW, she will actually be doing the cleaning under my supervision, she's very into this.)
posted by jbickers at 7:22 AM on December 10, 2014

If you add new water, make sure it's the same temperature as the current water. Don't want to shock the fish with icy cold water!
posted by erst at 7:28 AM on December 10, 2014

Ooh. Such bad advice from the pet store! Not surprised.

They need something like a 50 gallon tank - or larger, even at this size of fish - and the filter (a good strong filter, maybe even a canister) should be running 24/7, as when it dries out, the beneficial bacteria on the filter will be dying. The fish shouldn't be overfed, but neither should they be fed sparingly to get around the fact that they're in too small an enclosure (feeding sparingly to avoid waste is like only feeding a cat every second day so the litter box isn't as full).

I don't know if your kid will allow this, but can you take them back to the pet store and get something like a betta? Otherwise, and I know they're just goldfish, but you're kinda hurting them by forcing them to swim around in their own ammonia without enough space. Not a good example.
posted by Nyx at 7:35 AM on December 10, 2014 [2 favorites]

Response by poster: Hmm ... well, I can tell you that a 50-gallon tank isn't a possibility in our house. Also, secondarily, daughter is happy about the fact that she can keep the tank in her room, and only a small tank is possible in her room. Are there fish that thrive in such a small tank?
posted by jbickers at 7:39 AM on December 10, 2014

I prefer to clean the fish tank on a sunny, warm day. I do it only about every 2-3 months (less often during the winter as there are far fewer sunny, warm days).

Currently, I just have a plecko. But the tank previously held two HUGE goldfish, both of which have since gone down to Davey Jones' Locker. I don't think I'll replace them as I want to get rid of the fish tank -- mainly because cleaning and monitoring the tank is a big frustration for me. The tank is much cleaner now that the goldfish are gone, though.

This is a messy, disgusting process. Wear dumpy clothes when you clean the tank.

I use one of those five gallon buckets from Big Orange which is dedicated to this purpose and this purpose alone. I've also got a dedicated gallon pitcher.

I fill that bucket with the existing water in the tank, transferring via the pitcher. Then I unplug the filter pump and air pump and transfer the fish from the tank to the bucket.

I set the bucket aside, then proceed to take the water out of the tank pitcher by pitcher and either dump it down the drain (I've got a septic tank) or outside on the grass.

Once the tank is nearly empty (water just covering the gravel), I'll remove the tank decorations and discard any live plants that have died. If I'm replacing the gravel (which I only do about once every year or so), I'll do that at this time, throwing it out, and then removing all the remaining water using the bucket. I'll bring the tank outside with me if this is the case.

I bring all the tank decorations, air stone and hose, and the filter pump outside and lay them on the grass. I'll take the garden hose out and wash them with a sponge (dedicated for this purpose) and some soap. Make sure to rinse all the soap thoroughly or your fish could get sick. Ditto the tank if I'm cleaning that.

Now I'll dry everything off with a towel (dedicated for this purpose), put the decorations, air stone, hose, and filter pump back. Add new gravel if I'm replacing it, add new live plants. Add ROOM TEMPERATURE OR LUKEWARM tap water to the tank, pitcher by pitcher, until the filter pipe is covered enough for operation. At this point I plug the filter pump and air pump back in.

I have well water, so technically I don't need to do anything to my water for fish, but I do anyway. I add water conditioner according to the directions on the bottle.

Now I put the fish back in the tank, as well as one pitcher of the old water from the bucket. I dump the bucket on the grass or down the drain.

Done. What a pain.
posted by tckma at 7:42 AM on December 10, 2014

By the way, the guy at the pet store is an idiot (why am I not surprised?). Your filter needs to be running 24/7, otherwise the tank will get very dirty very quickly.
posted by tckma at 7:44 AM on December 10, 2014 [3 favorites]

Ugh, sorry, yes, Breanna is correct - don't run the filter pads under the tap.

Sorry about that.

I haven't actually had to clean out Chegwin in years - the husband does it now due to the heavy lifting involved in even cleaning out 20% of his water.
posted by Katemonkey at 8:34 AM on December 10, 2014

DO NOT USE A KITCHEN SPONGE. Not even a new one. I once killed a whole tank of fish this way. Kitchen sponges are treated with anti-mould, mildew, bacteria, whatever. It will kill your fish. Buy a sponge at the pet store if you think you might want to wipe the inside of the tank down or do anything else with a sponge.
posted by If only I had a penguin... at 8:58 AM on December 10, 2014

I would just like to strongly recommend getting some aquarium tubing and siphoning out the water over any other method of draining the tank.
posted by prize bull octorok at 9:30 AM on December 10, 2014

No offense intended to tckma, but that's pretty much the opposite of how one keeps fish alive, barring the plecostomus, which you can barely kill with a kitchen knife.

As aquarium-keeping stands now, we have filters to aerate the water and to keep beneficial bacteria going (the bacteria that break down waste products into less harmful materials). What you're going for, in the tank, is a healthy microecosystem that is more or less self-sustaining when you change the water to get rid of the fish by-products and the increasingly more concentrated minerals as the water evaporates.

Breaking down the whole tank means you obliterate the healthy ecosystem and force all the bacteria to build up again, which means huge spikes of undesirable chemicals (as the various bacterial blooms cycle through their lives) which can kill fish pretty rapidly.

(I'm simplifying this a lot, because I dunno if anyone's really interested in the ins and outs of cycling, but... yeah, do not scrub out your tank. Especially do not use chemicals like soap on anything in a tank. Eep.)

With regards to fish that can live in a 2-3 gallon tank, yes! Betta fish can and they live solo - they are really beautiful and come in different colours and fin shapes and most kids love 'em. You'll need to buy a little heater, but those are about $10 for that size tank. Bettas are very hardy and interesting to watch, and pretty smart, too - most of them can be trained to come to the top at feeding time. I really enjoyed mine and miss him (he lived a long betta life).

If there's room, you could upgrade to this kit (I own it and keep a couple of aquatic dwarf frogs in it), add a heater and keep five or six guppies, which are also really beautiful, colourful, long-finned fishes.

Both betta fish and guppies are less messy than goldfish and require a lot less space, so while you'll still need to do 25% weekly changes (that's the problem with a small tank - small aquariums are less stable and require more frequent water changes than large ones), you can safely get away with your little tank.
posted by Nyx at 10:52 AM on December 10, 2014 [3 favorites]

Why are you people all filling buckets with water manually? Buy a syphon for like £10 from the fish shop, best money you'll ever spend!

You should be changing about 25% of the water at a time, with the frequency decided by how much nitrate there is. You can buy tests at the shop.

The fish poo gets changed into ammonia, which your filter changes into nitrite, then nitrate. Each is less poisonous than the last. The filter can't do anything with the nitrate, that's why you do water changes to get the levels back down.

I'd recommend Bettas, but not Guppies, they are livebreeding fish, so you'll end up with babies all over the place.

I love Corydoras catfish, adorable little things full of personality that stay small, with maybe a few harlequin fish or tetras.
posted by chrispy108 at 11:01 AM on December 10, 2014

I have two African dwarf frogs in a ten gallon right now. They are the bomb (and completely aquatic, and super cute)! You could look into getting one of those for a three or four gallon tank. Alternatively, a betta would work. They're pretty easy to care for. Either way, you should really only get one fish for such a small tank. Any more than one and you'll need to change the water too frequently, as ammonia will build up more quickly.

As for the goldies: Since you haven't changed their water in months, any drastic water change will kill them. I'd suggest changing about 25% of the water your first time, and then do 20% changes every four to five days until their water reaches a better clarity, and hardly any waste is floating around. Then you can do anywhere from 15 to 20% every week or two. Never wait months. Ammonia and nitrates will skyrocket!

Nthing what others have said about getting a siphon/gravel vacuum. I bought a small sized one at PetSmart for ten bucks and it's really a necessity. Just grab a bucket, clip the bottom of the gravel vacuum to it, and start draining water. Focus on the grossest spots in the gravel. Once you've drained about 25%, dump it and prepare the new water. I use a gallon jug to prepare my water so I know the exact water conditioner amounts that I need, then I put the cap on and shake it vigorously. Water conditioner is really all you need. I also test the temperature in the jug with a floating thermometer and make sure that it is within a degree of the water currently in the tank. It gets easier to tell the more times you do it, or you could prepare your water earlier in the day or the day before so it can adjust. Then just add the new water to your tank, and that's it!

Rinse all of your tools and for the love of fish, NEVER ever use soap on anything! Running things under hot water and letting them air dry will sanitize everything enough for what you're doing. If you have a filter and your tank has undergone the nitrogen cycling process, you do not need to remove your tank decorations and rinse them. As another poster mentioned, this decimates your beneficial bacteria. Vacuuming your gravel too often can also do the same thing.

Seachem Prime is a great water conditioner, like LittleMy suggested. I had to buy a 1 ml medicine dropper on Amazon to be able to measure it out for such a small tank. I also have an API Water Testing Kit, as bettafish mentioned.

If you ever want to get a different tank inhabitant, look into nitrogen cycling several weeks before you bring home any new buddies. And if you have any questions about any fish-related things, feel free to shoot me a message on here!
posted by BreannaBear at 4:01 PM on December 10, 2014 [1 favorite]

Yeah, a single African dwarf frog or a single betta fish sound like your best options. A couple caveats:

1. Make sure you're getting an African DWARF frog, not an African CLAWED frog. Those are also cute, but grow huge.
2. Don't rule out female bettas! They have shorter fins than the boys, but are frequently more active and personable (probably because they don't have to drag heavy fins everywhere). If the pet store person sees you looking at the females they might try and convince you to get multiples -- ignore them. Keeping a betta "sorority" is technically possible for advanced keepers with a much bigger tank than you have available.

Because these are warm water options and goldfish are cold water, you'll need to buy an aquarium heater -- make sure to get one marked as being suitable for your tank size, probably in the 5-7.5 watt range.
posted by bettafish at 8:51 AM on December 11, 2014

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