Petco Text Logo
Petco Pet Logo

  • Two Easy Ways to Start Earning Rewards!

Why is my betta fish acting weird after a tank water change?

Updated On September 23rd, 2025

Pet's info: Fish | Unknown - Fish | Male

I just cleaned and changed the water in my beta fish tank. I have 1 male beta fish. Afternoon putting him back in the tank with new water, he seems to be acting differently. His swimming seems to be frantic, he is at the top of the water a lot, he was searching the rocks along the bottom, and he has bumped into the tank walls a few times. Did I do something wrong with his tank? Could his water be too hot or did I not condition the water right?!? Is this normal or is there something wrong??

This question includes photos that may contain sensitive content. Click to view.

View more to consider that the photos may include sensitive content.

2 Answers

Most Helpful Answer

Image profile

Answered By Dr. Dayna, DVM, CVA

Veterinarian, Certified Veterinary Acupuncturist

Published on September 18th, 2017

When performing water changes it is recommended to change about 15-25 %of the water. His helps keep some of the good bacteria in the water as well as decreases dramatic temperature changes which can cause significant stress on the body. I suspect that it is the temp change that is hard in him, however if a dechlorinator was not used in the water then that could be problematic as well. If you feel that is the case please Add a dechlorinator. I hope he improves!

Vote icon

2Pet Parents found this answer helpful

Related Answers from Veterinarians

  • Image profile

    Answered By Todd Cecil

    Veterinarian

    Published on January 26th, 2019

    Thanks for reaching out and sorry about your fish. Not sure if the cause of death can be identified but changing the tank would be a concern. Were water temperatures, pH, and addition of dechlorinator all checked prior to placing your fish in. Might have come with a disease or parasitic infection. Sorry again.

    Vote icon

    1Pet Parents found this answer helpful

See More Answers

Related Questions

Petco Pet Education Center
Health & Wellbeing
I have a veiltail male betta fish I did a hundred percent water change on him the water change was warm water he was in a holding tank with cold water and put him in he start acting erratic old darling running in the buildings and plants I took him o
The shock of full water and temperature change may be causing the clinical signs you are seeing now. With any luck, he will adjust and go back to normal. in the future with Wolverine or any other Betta, you should try to avoid doing 100% water changes unless it is absolutely necessary. Cycling the water weekly by about 25% is the best thing you can do to preserve the water your fish are used to.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
My betta fish is being mopey, he normally is active but since I changed his water last he isn't moving around as much. He's in an one gallon glass bowl that I bought from walmart. His water is at a constant 74-76 degrees, I keep everything consistent
I would recommend to change his water again and make sure you have a water conditioner that is not expired. I would also recommend to upgrade Smitty to a 3-5 gallon aquarium with a filtration system and a light. These tanks tend to create a healthier environment because the water is moving. You could add in live plants to provide a little extra oxygen. I hope Smitty starts feeling better!
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
I just cleaned my Betta fishes tank I put the same stuff as usual and a couple hours later he started just sitting at the bottom of the tank with his fins clamped together and now he's just sitting at the top and like vibrating his fins then clamping
Check the water quality in the tank/bowl. Do another water changed with "stale" water. This is water that has been left out for at least 24 hours which allows chlorine to dissipate. You may still need to add chemicals to deactivate chloramines which are used in municipal systems. Use a home test kit to test for ammonia, nitrates and nitrites or submit a sample for testing. Most pet stores or aquarists will do this for free or for a nominal fee. Check the water temp as well. Bettas do best in water that is 78 F to 80 F. It should not drop below 74 F. Use a small tank heater if necessary. A bit of aquarium salt should also be added to the tank at every change. Velvet is parasitical infection that may account for the symptoms you are seeing. You can treat/prevent it by adding aquarium salt. Pick up some BettaFix at your local pet store as well. Use according to bottle directions.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
I recently gave my fish a water change (halfway) for its 5 gal tank (relatively new tank). I made sure to treat it with conditioner and the tests came out ok. However my fish seems to be agitated and is swimming back and forth on one side of the tank
Did you change any of the plants or other features in the tank? That could be confusing him. It could also just be due to stress. Did you take him out while you changed the water or did you leave him in? Taking him out is recommended but it can still be stressful for him due to all the moving. Did you do a partial water change or a full change? Since I am not sure of what your procedure was it is hard for me to comment. I suggest you refer to this article about how to properly change the water to make sure you are doing it correctly. If you still have more questions please feel free to post again. ( https://goldfisho.com/goldfish-tank-water-changes/ )
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
My fish is bloated near the head and he won't swim. He just floats at the top and his fins hardly ever move. He only eats his food when it begins to float to the bottom of the bowl. His fins are pitiful and dull. He won't interact or flare his fins a
Check water temperature and chemistry. Bettas do best between 78 F and 80 F. Unless the room is very warm, a small heater is typically required. Without a filter, frequent water changes are necessary to prevent elevated levels of ammonia, nitrites and nitrates. All can be toxic to fish at high levels. Use only aged or conditioned water that is temperature matched to prevent further stress or shock. Plain aquarium salt (NOT table salt) can be used as a general tonic, to reduce stress, to treat minor infection and to aid in recovery. Dissolve 1 teaspoon of salt in a cup of tank water and gently pour it into the tank. Perform daily water changes, using aquarium salt for 10-14 days. If there is no improvement, consider a broad spectrum antibiotic. You can find one in the aquarium section of the local pet or fish store. Follow label directions carefully.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
Hi, I have a beta fish named Patron and recently he's been acting different. I noticed a few days ago that he has been laying at the bottom of the tank and only moves when I move him (he flaps his fins around a bit) but doesn't swim. I'm also really
Cold water can affect activity in fish. Bettas are tropical fish and do best between 78 F and 80 F. Check the water chemistry also. You can use a home test kit, such as the API Master Kit, or submit a water sample for testing. The local Petco may do this for free or for a small fee. Aim for an absence (0 ppm) of ammonia and nitrites with nitrates at 20ppm or less. Perform a partial water change if necessary to stabilize chemistry and/or to improve water quality. Use only conditioned water that is temperature matched to prevent stress or shock. Diet can influence color, so it is possible this is partly to blame for the color change. There are diets that can be fed to enhance colors.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
My betta fish is lying at the bottom of her quarantine tank. Her fins are clamped. She eats and moves but it not very lively. I just got her. She doesn't have stress stripes. Her quarantine is heated and I don't have a filter up and running yet. I wa
The stress of the move may be the cause. Of course illness, injury or parasites are also possibilities. Confirm proper water temp, 78-80 F is best. Check chemistry as well. Ammonia or nitrites are toxic. Set up filtration as soon as you can or perform partial water changes using aged or conditioned water that is temperature matched. Drop the water level to make it easier for her to surface until she acclimates and is more active.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
I have a male beta fish and he been acting werid for 2 days now. Usually he swimming around but he haven't been eatting and he always laying on the bottom of the fish bowl. Is there something wrong with him?
There is certainly something wrong but unfortunately these signs are quite generic and would require a quite radical but logic approach to be interpreted correctly. Begin by submitting a water sample for quality testing. Most pet stores will do this for free or a nominal fee. High ammonia levels, PH imbalances may be responsible for that. Oxygen concentration and quality of the filters should be determined as well. If water quality is good and there are no major imbalances, your fish should get examined to look for any sign of bacterial/fungal infection and eventually water should be treated. Please do not hesitate to contact us again on the forum or by requesting a consultation if you have any more questions or to discuss it any further.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
My male Betta fish isn’t moving
Check the water temperature. Bettas do best between 78F and 80F. Low temps can affect activity in fish. You may need a small submersible heater to maintain water temperature. Next, check water chemistry. You can do this with a home test kit or by submitting a water sample for testing. Most pet stores will do this for free or for a small fee. Confirm an absence (0ppm) of ammonia and nitrites with a nitrate level of 40ppm or less. Partial water changes may be indicated to stabilize chemistry and maintain water quality. Use only aged or conditioned water that is temperature matched to prevent stress or shock.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
Trying to figure out why my female betta died this morning. I had a male in the tank with her (with a divider). She was acting fine and eating. I did do a water change but I only but in “bottled betta water”. I also added a heater but I unplugged it
Drop the water temperature to 80 F. Bettas do best between 78 F and 80 F. The higher temp likely did not cause her death, but warm water holds less oxygen than cooler water. She may have been ill or old. She does appear bloated in the image. It may have been dropsy or other infection. Monitor water chemistry using a liquid test kit. They are more accurate than the strips. Tou can also submit a water sample for testing. The local Petco may do this for free or for a small fee. Aim for 0 ppm ammonia and nitrites with nitrates at 20 ppm or less. Try to keep the pH as close to 7 as possible. Bettas can tolerate acidic water, but changes should be gradual to allow time for acclimation.
Updated on September 24th, 2025
image
Have A Vet Question?

Book an appointment with the pros – our expert vets are here to help.

Book Now

Sponsored