This is an overview of how to set up and maintain a freshwater aquarium. There are some later notes about water parameters and fish choice, but it's mostly just a quick how fish tanks work page. I don't go in to exhaustive detail about anything, this is just the amount of info you should be able to get (but probably won't) from a good fish store.
Brand New Fish Tank | Water Testing and the Nitrogen Cycle| The Second Fish Tank | Maintaining a Fish Tank | Livestock | Acclimating Livestock | Quarantining (Isolating) New Livestock
This section is for a brand new fish tank, if you have an existing fish tank skip to the second section on how to set one up from an existing tank rather than from scratch.
An excellent starter fish tank size is about 30 gallons. The minimum I'd recommend is 10 gallons. The absolute minimum I'd willingly put a fish in is 5 gallons. 20 gallons is an okay medium, but the smaller the tank the less stable water parameters will be so if something goes wrong it will go wrong faster in a smaller tank.
Aquariums go on sale regularly at big box stores, often for 50% off. If you are buying a glass tank check all the edges for any chips or cracks before purchasing. I personally prefer large glass tanks to any of the tiny plastic “starter” tanks. The starter tanks are almost universally too small for fish to live in long term.
Note that fish tanks will weigh roughly 10 lbs per gallon, that’s the weight of the water, décor and tank combined. The larger you go the heavier it will be. Make sure whatever furniture you are using as a stand can accommodate that weight. You will want the tank as level as possible as well.
I have glass covers on all my tanks as fish like jumping nad I don't like fishng them out of the carpet or finding out the cat went fishng.
The basics of filtration is water is pumped over filter media mostly either to remove particulate matter or to pass by bacteria to break down waste in the water. Some “kit” type tanks will come with a filter area in the back of the tank, I consider this to be a sump style or an internal filter depending on how it’s set up.
I shoot for a minimum of 5 times an hour turnover, but prefer 10 times an hour turnover on a tank, so for a 50 gallon tank I would want 500gph worth of filtration. If the fish I have like current or are cold water I’ll up the gph higher. I had a 40 gallon with (2) 500gph power heads running the filtration once. The hillstream loaches I was keeping at the time loved the turnover.
This filter hangs on the back of a tank, pulling water up then cascading it back into the tank after running it through some filter media. Upside is most of these filters have plenty of space for media and can be retrofitted to accept reusable sponges instead of whatever disposable media the manufacturer provides. They want you to keep buying media. I generally cut filter foam sheets or blocks to fit whatever media section they have and run that instead of any proprietary filter frames.
Downside of these filters is if they overflow the water is outside the tank and they can keep pumping until they lose suction. You need to check them to make sure the media isn’t clogged and that they’re set level to the tank to prevent overflows.
Upside is plenty of aeration and biological area. Downside you need a separate air pump, hose and check valve to run it as well as it being loud. Other downside is the physical space they tank up in the tank and well, ugliness. They mostly can’t leak water out of the tank, either by putting the air pump above the water line, or making sure you use a check valve to break any suction if the pump stops running.
I use these on iso or quarantine tanks. Also good for grow-out. Not great for “display” tanks. Often used in fish stores so each tank is independently filtered.
Most of these are extremely under-powered. A tiny power head will pull water through filter media before pushing it back into the tank. The ones I’ve purchased always clogged fast and weren’t very good at their job of filtering. I’ve made custom ones just sticking a sponge on a power head. Those work decently well, but the sponge tends to clog fast.
Water is pulled from the tank, filtered in a separate box then returned to the tank. Most of these have decent media space and work well enough. I found cleaning them to be extremely annoying with filling and then getting them to prime (restarting the siphon/suction) was problematic for the one I tried. They’re also often the pricier option.
Most of these are used in Salt water. Essentially water is taken from the main tank, normally via an overflow system and dumped into a large filter tower which then drops into a sump tank with baffles and filter media or live plants to suck nutrients from the water. The water is then pumped back up to the main tank. Upside is the filter media space is massive, so it can filter a large system well.
Downside is since it’s outside the main tank leaks can be a problem, as can a broken siphon on the main tank. You want to be sure it is large enough to hold all water that can be siphoned from the display tank in case of a power outage.
This type I prefer even though it’s also ugly. Using a piece of filter foam at least 1 in thick and the height and depth of the aquarium I wedge it on one end. Behind it I’ll put the heater and a water pump. The outlet of the pump I’ll pipe through the foam back into the tank. So the water will flow from the tank into the foam, then back out by the pump. I install the foam before any gravel.
Upside, massive slab of filter, plants can grow on it, and it’s generally safe for shrimp and fish. Downside, ugly, so so ugly. The filter mulm will build up behind it and the pump will periodically need to be taken out and cleaned. It runs better if the pump itself also has a prefilter.
Tropical fish require heated water. A heater is still needed if you have a heated house because most tropical fish want a steady temperature of 75°F to 80°F. There are some cold water fish available in the hobby, but most of them would also prefer a heater just set lower to keep the temperature stable. The most well known cold water fish are goldfish, but they are mostly unsuited to tank living.
You will want an adjustable heater, not an “automatic” or "preset" one. Expect the calibration to be off and make sure to have a thermometer in the tank so you can check the heater is working correctly. Accept that you should check it periodically as every heater I’ve ever had (multiple brands and sizes) eventually went bad. If you’re lucky they just stop working, but many try cooking the fish first.
I prefer "natural" decor, so gravel or sand as a substrate, driftwood and rocks as decor. In iso tanks I'll sometimes have clay or plastic caves as hides.
This is just a special note, if you add driftwood from a pet store and don't read the label you'll be surprised when it grows white fluffy "stuff". This is bio film. It will go away, some fish and critters will eat it. It's harmless.
I use exclusively live plants since I pulled a chunk of plastic plant out of the gills of a clown barb many years ago. They do however add more mess and some fish eat them. If you prefer fake plants I recommend the softer silk kinds rather than hard plastic.
If you have any large rocks they should go in first, possibly with padding underneath between them and the tank to keep from a pressure point crack. Then substrate, gravel, sand or some kind of aquasoil. Gravel and sand I prewash, sand can take a lot but you want as much dust out before you put it in the tank. I don't do dirt tanks. Plants mostly get anchored to driftwood or into the substrate.
Place a plate or pour your water into the tank over decor to avoid kicking up the gravel. Heater goes in when the tank is full, plug it in after it's been in the water about 1/2 hour. Filter depending on kind should also be setup when the tank is fullish. I fill to the bottom of the plastic trim top pieces.
99% of municipal water will have chlorine in it, some will have chloramine as well. Fish do not do well with either of these chemicals and they need to be removed before the water is safe for aquarium inhabitants. Some water will also have heavy metals in it, but honestly most water safe for human consumption shouldn't kill common aquarium fish. If you're very committed you can probably find test results for your tap water online somewhere.
Either way standard "water conditioners" should make most tap water fine for fish. They work instantly. If you're nervous mix the conditioner in the new water and mix before you put it in a tank with fish. I refill after water changes with a hose and just put the conditioner in the tank as I fill and haven't had an issue.
You will want to watch for any alerts about your tap water. Such as hydrant flushing week which my town dowes twice a year is not a good time for water changes. If you get a boil water order I'd not use that water or the water for at least a week after when they likely dose extra heavy with chlorine.
Depends. It is better for the fish if you do a fishless cycle before adding them. If you load up the tank with lots of plants or did some of the shortcuts below you can get away with putting a very small amount of fish in the tank immediately. You will have to do frequent water changes to keep the water safe for the fish, but it's possible. It will make the entire cycle take longer though.
At minimum set the tank up completely, make sure the heater is keeping the temp stable and the filter is working for at least a few days before adding fish.
If your water has a pH between 6.5 and 8.5 you should be okay, though there are sensitive fish that will not be happy at the extreme ends of that scale. That said a pH between 6.5 and 7.5 is easier. The higher the pH often the harder the water. You should be able to get basic test results at any pet store.
A full test kit (pH, Ammonia, Nitrite, Nitrate, GH, KH) is good, and lots of people will say essential. I have one, but I'll admit I use dip strip tests to quickly see if anything is worrisome and do the liquid tests if I'm suspicious. So far I've checked back and forth and the results on my particular tests are the same. I use fish specific strips, not the random cheap no name pool dip test strips.
Fish produce ammonia as waste. That ammonia is poisonous to the fish in the long run. It will burn their gills and kill them if they're particularly sensitive. Cycling a tank is encouraging bacteria to grow that will convert the ammonia to less toxic nitrAte. It will first be converted to also toxic nitrIte.
There have been multiple "bacteria in a bottle" miracle tank setup products, and most of them are a complete waste. Your tank is not cycled until it has nitrAte and if ammonia is added it is converted to nitrAte.
You add a source of ammonia, fish food, cocktail shrimp, liquid ammonia, etc. and the bacteria all grows without stressing or killing any fish. It can take 4-8 weeks from start to finish. And you'll be looking at an empty tank with a cocktail shrimp slowly rotting in it. It's boring, but it works.
Get some of the "potted" aquarium plants. Keep them in the pots and don't wash them. You will likely end up with snails and other critters, but you'll also end up with some bacteria starts.
You can also just use lots and lots of live plants to cycle, but too many plants can sort of mask the tank being cycled as they will remove ammonia and such before the bacteria can grow to get it.
Mulm is the brownish gunk that ends up building up in filters. It's a gross slurry of bacteria and goop. Taking some from a healthy tank will kick-start a new tank. I'd dump it directly into filters. Gravel or other decor from an established tank can work in the same way.
I've seen lots of "Betta" plants and "Shrimp" friends sold in cups at various pet stores. These can be used to jumpstart a cycle, especially if they have a piece of driftwood or coconut cave attached. These make good bacteria sources. They're better if they're in a tank with fish, but the ones in the cups work as well and are less likely to give you snails.
If you absolutely can't get anything else tank water may help a bit. Not much though as bacteria isn't generally free floating in the tanks. It's on the decor or in the filter.
Don't change all the filter media at once. This will remove too much bacteria and you'll start a mini cycle when there will be ammonia or nitrite in the water to harm the fish. If you need to clean filter media swirl it around or squeeze it out in removed tank water.
Don't add lots of fish at once. Stick to small numbers for any additions, such as 6 small fish at one time.
Don't wash filter media in tap water. This will kill the bacteria.
Don't "scrub" decor aggressively to remove algae. Same as above, the bacteria lives on surfaces and in the filter. Some algae is fine and won't bother the fish.
Steal some filter media, steal some mulm, steal some decor. All of those will work. Add them to the new tank. Stock very lightly, feed lightly for a week or two. Test periodically, it should "instant" cycle with maybe a very small amount of ammonia or nitrite. I set up all my secondary tanks by stealing filter media from a set up tank and maybe some decor.
Once you have one tank, you tend to get another if the first succeeded. At my high point I had 20 aquariums going at once. Water changes were every Saturday and took a few hours. I had to break them all down when I moved and I'm up to 4 at my new house. Goal is 2 large tanks, 2 growout tanks and 1 iso. I have a 60 gallon I want to pick up then I'm done with acquiring for a while.
You can base this on water test results, you want Nitrate below about 40ppm. If you want fish to breed you want it lower. If it's too low you'll get lots of algae though.
When I had lots of tanks I did 25% to 50% water changes weekly. How much I did was dictated by a five gallon bucket being my water removal device. I also had a pump attached to a hose that I used for some tanks. Refilling I always use a Python water changer. I don't like the amount of waste to use it to drain, bu for refilling a hose from a faucet is a winner.
You will need a brand new bucket (food grade 5 gallon is easy to find), a hose and "gravel vac" the gravel vac is mostly to get a siphon started. just fill it with water with the other hose end in the bucket nad hold it verically until the water flows down, dunk it back in the tank before the water finishes emptying and it should start the siphon. If you don't have a hose, refill the bucket with new (temperature matched to the tank) water add conditioner and put it in the tank.
I don't care much about algae. If it gets excessive I'll pull it out or adjust the lighting times. I will use a razor blade to scrape the front glass of any tanks so I can see the fish. The sides and back I just let grow algae. The fish don't seem to mind and it's just another "plant".
For adult fish, small amounts every day is fine. If the tank has an algae problem cut back on feeding. If the fish are young and still growing out feed more often so they can reach full size. I use small sinking granules as my staple food, with frozen brine shrimp and bloodworms occasionally.
Be PICKY. No spots, no clamped fins, no rapid breathing, no bumps, no weird colors or messed up looking heads, no hanging out in a corner by itself if it should be schooling. Check all the fish in a tank, the ones you're interested in and all the tankmates. Make sure there aren't any dead fish, or picked apart skeletons in back corners.
If you're somewhere the tanks are connected check every fish in that rack (big box stores it's normally each column of 3-4 tanks that share filtration.) If the tanks are standalone still look around as diseases can be spread by nets. You want any sick tanks to at least be labeled not for sale.
With most of the schooling fish anyway you can try wiggling your fingers at the front of the tank to see if they swarm to the glass. If they do it's a good sign they're both being fed and eating. You can look for fish that aren't reacting and they could be sick if not recently delivered.
If possible don't buy fish the day they are delivered to a store. The store probably has a guarantee with the shipper that any 24 hr deaths are credited. If you happen to live somewhere that fish are harder to come by (my local stores sell out of anything interesting often the day after they arrive), be even more picky.
This is a short list of the fish we used to recommend when I worked in a fish store. It isn't a complete list, just fish that had a good chance of not immediately dying. All the schooling fish do better with more, like lots more. These are also the fish more likely to survive started tanks with beginners.
Peaceful (unlikely to pick tank mates to death, either because they're actually peaceful or just too small to kill anything...)
Semi-Aggressive (these guys will kill off or harass smaller more peaceful fish, but they tend to be lively)
I consider all catfish types and anything wild caught to at minimum be in this category. They're slightly more picky about water staying stable. Corydoras, guppies, mollies, loaches, danios, and pickier tetras like rummynose are all in here.
Also known as the fish more likely to "die for no reason". This is more common for wild-caught species as well as fish known for being picky eaters. Though some people will disagree I also stick Neon Tetras in this cateogry. I've never had luck keeping them alive.
They get big, they're horribly messy, they love eating plants, and they're often unhealthy to start, especially the "fancy" types. Goldfish need about 20 gallons per fish, the comet types do best with lots of swimming space. The smallest tank I've kept them in was a 40, but they do better in ponds. They just get too big and are too messy for most fish tanks.
Largest predator I ever kept was an 8" mutt (malawi mix maybe) cichlid, and he had a 55 with a ropefish and a large pleco and nothing else. And he was still too messy. In general you're looking at a 75 gallon tank with 2-3 fish. That's why I stick to smaller fish as they're less of a load on the tank so there can be many more in a giant tank.
Just don't. Most tanks do not have the correct kinds of algae to keep one fed and if they survive they can become massive. Like goldfish they're particularly messy and add a lot of bioload to a tank.
I've never had luck with the larger snails, mystery, apple and ramshorn. I've kept nerites alive for a bit, but mostly I stick to "pond" or bladder snails, the smaller ramshorn and trumpet snails.
I've kept cherry and amano shrimp alive for a bit, but they have more narrow water parameters that I don't often have. And my fish like eating them because that's where they are in the food chain.
Most will eat fish so I've never really kept hem. Even the dwarf ones will eat anything they can catch and they normally go hunting at night.
Any fish you buy you want to temp-match to your tank, and sometimes you will want to add water from your tank to the bag to equalize the water before you add the fish. You generally DO NOT want to add any of the bag water to your tank if you can avoid it.
Turn tank lights off, float bag in your tank for 20-30 minutes. Open bag and add some tank water to it, close back up. Do that a few times. When bag water has doubled you can dump the water and fish into a net and put the fish in the tank. If the fish are known for being a problem to net (catfish, hillstreams, loaches for example) drain as much water from the bag as possible before pouring into the tank.
This assumes the fish were in the bag for a maximum of a few hours. If they've been in the bag much longer switch to mail-order instructions.
Sometimes you can't find what you want locally, especially if you live in the middle of nowhere. Expect more losses with this source.
Turn tank lights off, float bag in your tank for 20-30 minutes. When the bag is the same temp as your tank, pour the water and fish into a net over a bucket and put them in the tank. The bags are full of ammonia and opening them will make it more toxic so you can't slow acclimate the fish without the water injuring them.
Most of these you acclimate like fish from a local store. Some of them need to be drip acclimated, which just means pouring them into a bucket and using a knotted airline tube to slowly drain tank water to the bucket. When the water is maybe tripled they can be netted or scooped into the tank.
My existing fish don't get to meet any new fish until they've lived disease free for 2-3 weeks. Doesn't matter where I bought them or how long I saw them in the store.
10 gallon bare tank with some live or fake plants and a large sponge filter. Depending on species, maybe a cave or other bottom decor for hiding. I like a 10 gallon as most medication is dosed by 5 gallon increments.
Wow that sounds morbid... but it's true. This is mostly addressed to recently purchased fish. I personally count any fish that die within the first two weeks of purchase to be not specifically my fault. Shipping is stressful, changing water parameters is stressful, many distributors don't even feed the fish if they can get away with it. This is just how it works. It's even more likely for "rarer" fish. They could have sat at a distributor for longer and just not been healthy enough to ship.
That all said I will try treating any fish I buy, if they come down with ich or other easily identifiable and treatable illness. Some fish should be prophylactically treated for parasites just because they're known to have issues with them. Any goldfish I ever bought I treated for body fungus because they almost invariably had it.