Why is my betta fish mopey and not moving after a water change?

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!

The first thing that needs to be done is a water quality analysis. If you don't have a test kit, most pet stores sell a basic test kit that measures pH, ammonia, nitrite and nitrate. If any of those are amiss, correct that problem. Laying on the bottom of the tank is often a sign of swim bladder disease. This could be an infection, fluid accumulation or a mass pressing on the swim bladder. All of these create a situation where the swim bladder can not contain air, that allows them to control their buoyancy in the water column. The best treatment for this is seek assistance at a veterinary clinic with experience with fish, and have systemic antibiotics prescribed. A radiographs would be helpful in diagnosis. A good fish veterinarian would probably be able to aspirate the swim bladder and collect a sample for diagnosis. The majority of antibiotics available for fish over-the-counter are not good for internal infections and could possibly make things worse. Good luck.

That looks like a very small tank for sweet Cherry. Bettas really do best in a larger space, I would consider 2.5 gallons the absolute minimum. The larger the tank, the safer the water conditions will be. They also need a filter and water heater. They are tropical fish and really need the water to be 78-80*F. Hopefully this is just a husbandry issue rather than a disease. Check out this article for more advice: https://vetmed.illinois.edu/pet_column/betta-fish/

He is "old" for a Betta. Check the water chemistry and temperature. You can use a home test 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 partial water changes to stabilize chemistry and/or to improve water quality. Use only conditioned water that is temperature matched to prevent stress or shock. Bettas do best between 78 F and 80 F. The cloudy eyes may be due to infection. Maintaining pristine water quality will help, but you may need a broad spectrum antibiotic as well. Look in the aquarium section of the local Petco for medication. Follow label directions carefully and remove the carbon filter insert during treatment if indicated. Even with treatment, there may be permanent damage to the eyes if the condition has been chronic. The "laying down" is sometimes seen even in healthy fish. They may choose to lay on gravel or the broad leaf of a plant. It may also indicate infection or injury though. If hebisbhavibg difficulty reaching the surface, decrease the water level to make it easier. Bettas need to surface occasionally to get some air.

Recheck water chemistry to confirm 0 ppm ammonia and nitrites with nitrates at 20 ppm or less. A pH of 7 is fine and they can adjust to more acidic water as long as the change is gradual. Temperature should range between 78 F and 80 F. Plain aquarium salt (NOT table salt or epsom salt) can be used as a general tonic to reduce stress, improve gill function, treat minor infection and aid in recovery. Dissolve 1 teaspoon of salt per gallon of water in a cup or two of tank water and gently pour it into the tank. Perform partial water changes every couple of days to maintain water quality. Treat only the volume of water being replaced. Treat with aquarium salt for no more than 14 days then reassess the condition. An antibiotic, such as kanamycin or erythromycin, can be found in the aquarium section of the local Petco if the salt treatment doesn't help. Follow label directions carefully and remove the carbon filter insert during treatment if indicated.

Check the water temperature. Bettas are tropical fish and do best between 78F and 80F. Low temps can affect activity in fish. If temperature is normal, check the water chemistry and perform a water change if necessary. Use only aged or conditioned water that is temperature matched to prevent stress or shock.

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.