URGENT: beloved dojo loach has unknown illness

[suzanneisalive]

Hi everyone! One of my dojo loaches named big mama has come down with an illness and I need help diagnosing it and figuring out a treatment plan. I have had a lot of trouble sorting through conflicting advice on other forums, so I'm hoping to get some clarity on here. She is a large loach, about 7-8 inches. The tank she is in is a 55 gallon breeder tank and it has 3 other smaller dojo loaches and a dwarf blue guorami. She has definitely outgrown the tank and I am trying my absolute best to get a larger tank, but it's been hard to find a 75-100 gal tank that is within my price range.

The water parameters are: 

Nitrate: 25 ppm Nitrite: 0 ppm Buffer: low, 40

pH: between 6.4 and 6.8 

My house does have pretty hard water

Chlorine: 0 ppm

(I'm doing another water change after I post this to get nitrate down again)

I started to notice the illness when she started having these crazy bursts of energy about a week and a half ago in which she would shoot across the tank and splash in the water, and it escalated to her jumping out of the tank, which has never happened before in the 3 years that I've had her. After she jumped out of the tank I did some frequent water changes because the PH had gotten somewhat low and I assumed a decrease in the water quality had caused her behavior, and now the water chemistry is somewhat better but she is exhibiting new symptoms.

She has been floating around the tank and generally acting like a depressed loach. When I got my first dojo loach, I didn't realize how social they were of creatures and it kept playing dead  (floating listlessly), so I did a lot of research and got more dojo loaches to keep it company--after that the loaches rarely played dead. She is exhibiting this same behavior, so at first I wasn't sure if she was sick or if she was depressed/unhappy in her tank and needed more space. However, in the past couple days she has been also laying upside down or on her side in the tank which is very concerning to me and indicative of a serious illness. She has no visual indicators of illness on her body as far as I can tell, but she has absolutely no energy and has been laying in these strange positions. There was one day in which she was floating a ton and it appeared to be a swim bladder problem as she kept floating back to the surface and it seemed like she couldn't control it, but that was just for one day and now she's back to laying at the bottom of the tank on her side or upside down (pictured). 

I've been trying to do as much research as possible and I've read that loaches can have adverse reactions to certain bacterial remedies/treatments as well as not doing well with aquarium salt, so I haven't treated her with any medications yet because I don't want to make her condition worse. I did read that feeding loaches peas with the skin taken off can help with constipation and ease swim bladder disorders, so yesterday and today I fed all the loaches including her peas, and they all enjoyed them. This morning she was laying upright for a while so I thought maybe it helped, but alas she is back to laying upside down. I have also not fed any of the fish in the tank their usual food for the past two days since I don't want to make her constipation (if that's what's going on) any worse.

One other thing that may be relevant to diagnosing her: around the same time she started exhibiting weird behavior I did introduce a new large plant to the tank, but I did a hydrogen peroxide solution dip to try to eliminate introducing any disease to the tank. It's possible the hydrogen peroxide dip didn't 100% work, but I thought I did it properly.

My question is basically-- is this how a swim bladder infection usually presents in dojo loaches? Should I move her to an isolation tank and treat with a specific medicine? Or should I just continue with frequent water changes and feeding peas? The only isolation tank I have is only 20 gallons and I worry that tank will be too small for her/it will be stressful for her to be moved.

Thank you so much in advance for any advice, I appreciate it so much! I really want to help her recover and see her doing well again.

[Colu]

Disorders of the   Swim bladder  cause abdominal swelling abnormal swimming behaviour loss of neutral buoyancy with fish either sinking to the bottom or floating to the surface that can be caused by the fish over eating and the stomach putting pressure on the swim bladder an injury to the swim bladder a bacterial infection of the swim bladder @suzanneisalive