Fishkeeping can be a difficult hobby to master. Not only do you have to learn about the wildly different needs of fish species, but you also have to manage a carefully balanced, miniature eco-system.
And just when you think you have it all figured out, you learn something you’ve been doing dutifully for weeks – or even months – has been harming your prized fish. Needless to say, this can be disheartening, and to help you avoid this, I’ve compiled a list of the most common mistakes people new to the hobby make when caring for their fish.
1. Feeding Your Fish too Much
Let’s face it, fish aren’t nearly as interactive as a cat or dog, so it’s only natural to look forward to feeding time – one of the only times you truly get to interact with your fish. After all, who can resist a fish begging for food along the front of an aquarium And what’s the worst that can happen?
Unfortunately, overfeeding fish doesn’t just lead to obesity – it often leads to illness and death. When you provide a fish with more food than they can eat, the food sinks to the bottom, where it starts to decompose. And when it decomposes, it releases harmful chemicals into the water.
Usually, if you only overfeed a little bit, the beneficial bacteria can handle the additional load (if you want to learn more about beneficial bacteria, read The Complete Guide to Cycling). But when you consistently overfeed fish, ammonia and nitrites start to build up unchecked, and you quickly end up with a real problem on your hands.
So no matter how much your fish beg, you need to limit the amount of food you provide to your fish. A good rule of thumb is to feed them as much as they can consume in three minutes. Any more than that, and you’re probably feeding them too much. If you want to learn more about feeding your fish, read How Much and What to Feed Aquarium Fish.
2. Not Using a Filter
While the idea of not using a filter would seem ludicrous to a more experienced aquarist, it’s actually fairly common for someone new to the hobby to be unaware they need one. Underpaid, under-experienced pet store staff don’t do a great job of making sure you’re prepared for when you take your first fish home, and unless you know where to look online, you may not even realize how integral a filter is to a fish’s health.
While there are a few setups that will work without a filter, most notably a Walstad Planted Tank, most of the time, if you don’t have a filter, at best you’re condemning your fish to a shortened life. At worst, you’ll be forced to watch as fish after fish goes belly up.
What is difficult to see in an aquarium without a filter, is the slow build-up of toxins that will first injure and then sicken fish, before finally killing them.
A filter allows a limited nitrogen cycle to occur, and beneficial bacteria growing on the filter converts harmful chemicals like ammonia and nitrites, into less harmful nitrates. Nitrates which can then be removed during water changes.
If you don’t already have a filter, then it’s something you need to get right away. I’d personally recommend an Aquaclear Power Filter, but no matter which filter you choose, it’s one of the most important components in a healthy fish tank.
3. Not Treating Tap Water
This is something that comes up quite regularly when talking to people new to the hobby – they don’t realize they need to treat their tap water. Now, not everyone needs to treat their tap water. Most wells don’t have chlorinated water, and in rare instances, certain water supplies use ozone, not chlorine to treat their water. If you have either of these water sources, you probably don’t need to treat your water (though with well water, you should test it for harmful metals).
But if you do have chlorine in your tap water, or chloramine, then you absolutely must treat it before adding it to an aquarium. Not only can it injure your fish, but it will also kill off the majority of the beneficial bacteria in the tank. The loss of bacteria will cause a spike in ammonia and nitrites, and it’s doubtful already weakened fish can survive a mini-cycle.
To treat your tap water, all you have to do is add water conditioner. A good choice is Tetra AquaSafe Plus Water Treament, which not only neutralizes chlorine, cloramines, but also heavy metals that can be harmful to fish
4. Incompatible Tankmates
Introducing incompatible tankmates is one of the greatest problems aquarists encounter at all levels of experience. Even when you think you have fish that should get along, a normally docile fish will start to act aggressively, or a species of fish that usually rules over a tank, is attacked and bullied into submission.
But when you’re still relatively new especially, it can be hard to figure out what fish go well together, and while pet stores have been improving in recent years, they often recommend fish that have no business being together.
If you have one fish that is constantly attacking others in the tank, then you could be harming your fish by keeping them together. Overtime, attacks can lead to heightened stress, which often leads to illness. And that’s assuming there’s no real damage from the attacks, including torn fins, or lost scales – both of which can become infected.
It’s important to keep an eye on an aquarium after adding new fish, and to have a backup plan in place in case things aren’t going well. And before adding any new fish, do your best to find out if they can co-exist peacefully together.
5. Not Changing Aquarium Water
I was recently exchanging e-mails with someone, who complained his fish were constantly flashing (high-speed rubbing) on the gravel and ornaments in his tank. After he sent me some pictures of the fish, and I was able to rule out the most common culprits like ick, I asked him how often he changed the water.
What I received back was the e-mail equivalent of a blank stare, and all it stated was, “change the water?” And surprisingly, this isn’t an unusual response. Many people, both new and experienced, don’t realize they need to change a portion of their tank water every week.
When you don’t change the water, nitrates continue to build up in the fish tank. While nitrates aren’t harmful to your fish at lower concentrations, they can start to irritate fish as their levels rise, and can cause increased stress and illness.
A good rule of thumb is to change 15% of a tank’s water every week, though you can safely go up to about 30% a week without encountering any problems. And always make sure to treat any new water being added to the aquarium.
6. Putting Unsafe Objects in the Aquarium
There is a simple rule experienced aquarists live by: don’t put anything in your tank that you don’t know where it came from. Whether it’s live foods, or rocks, if you don’t know the history of the object, don’t let it touch your aquarium’s water.
Of course, this isn’t something most fish keepers know, and I constantly hear from people who’ve added something new to their tank, only to experience a disaster of biblical proportions. From toxic rocks, to live foods contaminated by pesticides, the list is endless and heartbreaking, as people see their years of hard work wiped out almost overnight.
Always stick to objects you personally collect, or purchase from a reputable pet supplier. Anything else is just too risky to add to your fish tank.
7. Adding too Many Fish at Once
If you’re familiar with the cycling process, then you already know it’s a bad idea to add too many fish at once (read more about cycling here). But many people new to the hobby only vaguely know about cycling, and they often make the mistake of dumping new fish in, all at once.
Unless you have a reason for adding all of the fish at once – like you’re trying to setup a tank with highly aggressive, territorial fish – then you should only add a handful of fish at once. With smaller fish, a good rule of thumb is to add no more than three at once, and with larger fish, only one at a time.
This gives the biological filtration in the tank time to adjust, and prevents a mini-cycle from occurring – something no fish keeper wants happening. When you add too many fish at the same time, it overwhelms the biological filtration, and you’ll have a spike of ammonia and nitrites.
Final Words
These are a few mistakes people commonly make without realizing it, but thankfully, all are pretty easy to remedy. Like any other hobby, in fishkeeping, you learn from your mistakes. And you hope you don’t hurt any of your fish in the process.
Let me know in the comments some of the mistakes you’ve made without realizing it in the past.
Well my mistakes started when I bought a 2nd pleco and an angelfish from my LFS I dumped them water and all in my aquarium, the Angelfish didn’t last another hour, after two days the rest of my fish had white spots all over them, to top it off the medication I bought killed all the good bacteria forcing the tank to cycle again. Sad to say they all went belly up goldfish and guppy. What was left was both my common pleco. Well now I just have 1 pleco since they kept fighting and the new one died. Lastly I just found out that Common Plecos aren’t supposed to go in 15 gallon tanks since they can grow up to 18′. I’m so freaking lucky 😑
I’m a new aquarist 3 mo old.
UGF – 15 gal tank
I now have 7- zebra Danios
1 angelfish 5 tiger barbs 1 common pleco
Ouch, that’s a painful mistake. But I think we’ve all been there before, and I wiped out an amazing tank of platies doing the same thing years ago. But you learn as you go in the hobby. Hopefully you have some better luck going forward.
Thanks for the encouragement, I would really like to be successful in this hobby. I’m learning to love fish. I just wish I had read your blog before becoming a fish killer >.<
Just stick with it, keep reading, and keep buying bigger tanks. You’ll be an expert in no time. 🙂
What would I do with the old tanks?
When you find a solution, let me know. My basement is full of old tanks. lol
But as I grew, I kept many of my old tanks running, and just started new ones. It gets addictive very quickly, but just make sure you don’t burn yourself out.
My friend told me to make it into a sump for a liquidized bed. Unfortunately I didn’t get a chance to ask what he meant by sump or liquidized bed since he was in a hurry and we hardly see each other. As far as I know there’s only ugf canister hob and sponge attached to a power head. Maybe he was talking about a plant aquarium or saltwater perhaps?
You can turn old tanks into sumps for filtration. I’m hoping to write an article about that in the near future.
Hi Robert could you please help me to identify to snails that appeared in my tank after I bought a new Plant?? I am stuck–The 2 snail are conical and stripey and have laid hundreds of eggs in blobs on the walls of the tank–They have spent alot of time stuck together (mating?)—They do not burrow but spend time floating upside down on the skin of the water–as an aquarium novice I am completely lost–Any help eagerly awaited
Kind regards
Joanna
Sounds like pond snails.
Conical stripey snails (black and yellow) could be assassin snails. They have male and female snails that mate in a way similar to what you describe. They usually lay single white, almost square eggs on plants. These snails don’t eat plants, they eat other snails and aren’t a pest – people actually buy these deliberately.
Another conical snail is the Malaysian trumpet snail but these usually reproduce by live bearing (the females don’t need a male to produce young) males are extremely rare. I’ve never seen eggs from these snails and I have hundreds in my tank. These can be a pest or can help aerate a sand substrate as they burrow in the sand. They don’t normally eat plants unless they are starving. They prefer rotting matter and leftover fish food.
Pond snails are usually dark brown and not striped. Rarely they come in other colours. Their shell is kind of oval shaped with a small spiral point, not really truly conical. They lay multiple eggs in batches I believe (looks like a clear jelly like blob on glass). These snails eat plants and are a pest.
Physid snails look like pond snails but they are usually light brown or dark yellowish (often with dark spots). Rarely other colours. They move very quickly for a snail. They lay eggs like the pond snails. They can eat plants but usually prefer algae and leftover food.
Ramshorn snails look like a spiral (like a tightly coiled ram’s horn). They are usually reddish brown but can be bright red, blue, dark brown, yellow, orange, pink or clear. These snails can be a pet (people breed them for colour) or a pest. They lay eggs in small batches and usually eat algae and fish food but can eat plants if they get hungry enough.
Other snails worth mentioning : “rabbit snails” (conical – look like large trumpet snails), nerite snails (rounded she’ll, can be spotted, stripey or solid coloured) and apple snails (rounded shells – can be very large).
You could look up pictures of the different types of snails to figure out what type you have – it can be hard to get rid of pest snails once you have them. Some are almost impossible to kill without harsh chemicals or copper (not something you want in your tank if you can help it).
Great post!
Thanks. I’m glad you enjoyed it.
I made the mistake of adding fish too quickly with my betta male. He was fine with the first 2 cory cats but added 4 tetras a week later and I saw he was stressed by their activity and died before I could get a second setup…
That sucks, but bettas are notoriously hard to find tankmates for. I’ve tried a few setups myself, and the betta always ends up beating up his tankmate, or getting his fins nipped.
Hi. What tankmates would you suggest with bettas? I think a school of neon tetras would look supercool with one.. but i dont think that they are compatible…
Bettas are incredibly hard to compatible tankmates for. They are either bullied and nipped at, of they do the bullying themselves. For the most, I’ve given up on finds tankmates for them, and usually just keep them with large snails like mystery snails, or something else interesting like shrimp (though they may sometimes prey on smaller shrimp).
Hello! I just finished the article and swam down here to see if there was anything interesting. I think I can help with the betta problem.
I personally love betta fish, they’re my favorite (I even get betta kisses sometimes!) and what I’ve found is that it really depends on what betta you get who they can live with. I’ve managed to pick out the most mellow betta in existence so far. Right now I have a 10 GAL with a school of tetra, 3 kuhli loach, and 1 betta.
My tank is very peaceful as the kuhli’s squiggle around and the tetra swim around. The Betta likes to play with the water heater and the filter but doesn’t bother the other fish. I’ve also had success with a Betta and Angelfish, two species that (at the time I was unaware) should NEVER go together.
Normally I test out the beta’s personality by simply picking up his cup. If he tries to bite me I put him back down, if he lols about peacefully I pick him to come home with me (Monitoring his reactions to being moved to make sure he wasn’t just shocked into stillness the first time.) Some fish you can’t do that with but betta fish are easy since they’re normally in single cups. I hope this helped.
I’ll keep my out for that. Can’t wait to see how you can turn an old tank into a filter hahaha
Its called a sump.
Hi again Robert–Had another look at the snails they are not stripey-? Silly me! the colour is brown with black patterns in the shape of scales/squares effect—What are they please–Thanks…
Could you send me a picture of the snails? admin@aquariumtidings.com. That would be the easiest way to identify them.
Local schools will gladly take the tanks. Hastings high school in Houston (alief isd) contact the aquatic science or environmental science teacher.
Some fish such as gouramis do better with no filtration or circulation, or at most very slow currents. Using the low tech planted method, over filtration and doing too many water changes is considered not the best for it. Depending on the tap, it is more often than not fine to use tap with no water treatment – these conditioners are money makers for fish stores.
Note – this is using the low tech planted method. Plants clean the water, fish feed the plants. This is the method i use with great success. Almost no maintenance required except top off with tap water, and the tanks look great, fish and plants are very healthy for years!
It takes time and keeping on keeping on, there are many ways to keep aquariums and fish!
That’s an excellent point regarding gouramis.
When you say you can avoid conditioners, do you mean for people who have chloramine in their water? Because if you avoid the conditioner with water that has chlorine, you’re going to have a bad day.
Hi, I just set up a new 36 gallon tank, and bought two plants and zebra danios. I’m quarantining the zebra danios, but I put the plants straight in after rinsing them. I wanted to know, should I have quarantined the plants as well? If so, is it not too late to pull them out now and do so?
You don’t need to quarantine the plants, but I recommend dipping them in an about 1/20 bleach solution. This will kill anything on them, including any snail hitchhikers. Just makes sure to thoroughly rinse them after the dip, and then you should be safe with the plants.
Hi! i have 2 koi and a black shark (its as big as my koi only) I have been having some problem with algae on the walls of the aquarium. I read many articles and found that its better to have snails but my local pet store doesnt have any so what would you suggest?? I read many pages and it said that mollies are good too ?? I have already tried the chinese algae eater it didnt work …
The two best algae eaters I’ve found are bristlenose plecos, and Malaysian trumpet snails. However, plecos are great with koi for the most part, and you might find them sucking off the slime coat, though this mainly only happens with common plecos. It’s not as common a problem with bristlenose plecos.
Malaysian trumpet snails are usually pretty easy to find, and all you have to do is go to the local pet store. They will usually have them on them crawling on the glass, and most stores with give you some for free.
And just so you know, koi do better in cool water tanks, and they grow monstrously large. A commonly recommended tank size for them is 1000 gallons, and you might need to put a plan in place for when they grow larger.
Thank you so much but my pet store gave me a magnetic scrubber kinda thingy and it cleans so good .So i guess my algae problems are done with but anyways thanx for the advice 🙂
I quite like those magnetic scrubbers, and I’m glad my info helped you.
Hello Robert, Great article! My question is this, I have been in the freshwater hobby for decades…however im facing this greenish blue algae blanketing my substrate and plants, nothing on glass. My pleco wont touch it and my water parameters are 0/0/5ppm. I also have a uv sanitizer. How should i go about this, nerite snails? What is your expert opinion.
Thank you for your web service.
It sounds like a cyanobacteria outbreak in the tank. It can be a pain to deal with, especially if you don’t want to use antibiotics for it. But one way to deal with it is to increase water changes, and do as much manual cleaning as possible. Nothing else will really help, and the key is reducing phosphorus in the aquarium.
Cyanobacteria it is, and nothing will eat it. This is actually a bacteria that can photosynthesize, and not any kind of algae, thus can be killed off by antibiotics. One popular method is to use erythromycin in the tank. I once had this rampant outbreak of cyanobacteria, and I used this product called ” ultra life”, and inside a week the tank was clear. The thing never came back. Importantly, it is also very useful to avoid having dead zones in the aquarium with very little water flow. A good flow in the aquarium will discourage the growth of cyanobacteria.
The use of erythromycin or ultra life will increase the biological oxygen demand of the aquarium, so having one or two airstones going all the time during treatment is very important.
I maintain a good flow all around the tank now, and hopefully this primordial scum will never be back.
Hope this helps, and good luck.
I have had 4 tiger barb fish and one of them just died in a day they are in fish bowl and are moving near surface of water . What should i do
They really need a larger aquarium. But until you can move them, at least add a small sponge filter, or an air stone which will help. And step up the water changes, and be very careful not to overfeed.
After about 40 years of keeping aquaria, I would say the biggest mistake a fish keeper can make is not having, and learning to use, a high quality water test kit. I use the API Master Test Kit. Don’t waste time and money on the strips. When you notice problems with your fish you can test the water to get an idea of what is going wrong. Most often it’s a spike in ammonia or nitrites. I always test before doing a weekly water change (gives an idea how much water to change or if you need to do it twice) and two days after changing the water. Sometimes you get hit with a mini cycle and this helps to catch it right away.
Second big mistake is not researching species *before* you acquire them. Even fish in the same family that look almost the same have different requirements, which you may not be able to provide in your tank. Corydoras catfish are a good example of this – an Arcuatus (skunk cory) has much different requirements than a Trilineatus (three-lined) even though you often find them together in pet shop tanks. Corys are shoal fish and do best when there are 6 or more, but shops sell them singly or in pairs. Today I even saw “mix and match” Cory’s, being sold together but from three different species with different needs. Another example is brackish water puffer species. They throw green spotteds, figure 8’s and pea puffers in a freshwater tank with livebearers (Mollies) and the novice assumes they can toss the puffers in with their tetras and guppies. Sure, if you don’t mind your fish being full of holes/dead! Then the puffers don’t last long because they need brackish water and because the three species don’t get along.
This is all really great information. I used the strips for far too long when I started, and difference between those and the test kits are night and day. I immediately diagnosed a tank that hadn’t cycled properly and was finally able to get the fish healthy in there.
And it’s painful seeing how so many fish end up in conditions totally unsuited to them – although a lot of this can be blamed on over-eager store employees. I was at a store recently where someone was being sold Kenyi ciclids to go with fancy goldfish: That was going to turn ugly quickly.
Twenty years ago my dad had a room filled with fish. I remember helping him with them. Now my four year old son talked me into a beta. Then we got another beta. Then two neon fish. Now two oscars. But before the neons and after the betas we got a ten gallon tank and two big fan tailed goldfish. I hadn’t set up a tank in ages and my kids were trying to help but mostly just make it harder. I put pump in tank and electrocuted poor goldfish! I didn’t even realize I had done so until I put my hand in tank and got a shock from hell! Poor fish were dead before I could unplug pump. Kids kept saying look the fish are sleeping. Epic fail!!
lol…while I haven’t had the misfortune of almost electrocuting myself, we’ve all made mistakes keeping fish. But I think just about everyone who visits here can understand the addictive nature of keeping fish. I started with goldfish, and then somehow ended up with a room full of fish. I feel like I should be attending Aquariums Anonymous.
What would be good in a community tank with guppies and plattys
What’s your water pH and hardness? Also, how large is the tank?
Ph sits at a 7.8 and it is a ten gallon
In a ten gallon, you definitely don’t want to add any more fish. You’re already pretty close to being overstocked. But if you upgrade, fish like rasboras, zebra danios, and other live-bearer fish would probably work well – though you need to keep them in larger groups so they don’t nip the guppies.
OK did you ever get my emails thank you for the tip if you haven’t got my emails then I have a platty that floats on the top of the water but is still living what should I do
Is it bloated at all? Have you checked your water?
First of all, try feeding it some lightly boiled and shelled peas. If it’s a swim bladder problem, it might clear it up.
OK I checked the water and every thing I fine also not bloated at all as far as I can tell. Can I send you a pic over email
Sure. Send it to admin@aquariumtidings.com
I’ve just obtained a 75 Liter (80 Galleon) tank and I’m wondering what kind of filter to get, it will have 12 neon tetras and 4 cory cats
I’d probably go with either an Aquaclear hang-on-back filter, or a Fluval canister filter. It depends on your budget and while the Fluval is better, for your fish you’re probably alright with just a hang-on-back filter.