Help my silver dollar fish is struggling to swim and I don't know why

[ragz]

Hi, I have had 4 silver dollar fishes for about 5 years now and one of them looks like its struggling to swim. It has been laying sidewards at the bottom of the tank. The other three are energetic and swimming fine. I have just fed them and it managed to swim normally to eat but then after 30 seconds it seemed to not have an energy and is back to lying at the bottom of the tank.
It is not swimming upside down.

 

[Barry Tetra]

Hello and welcome to the forum. Can you post a video about it? You can post a video by upload it to youtube, copy and paste here. Also whats your water parameters? and when did the last time you do a water change?

 

[Colin_T]

Post pictures and video of the fish swimming and then sinking.

Test the water for ammonia, nitrite, nitrate and pH.

Do a 75% water change and gravel clean the substrate every day for a week or until we work out what is going on.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.