Whats wrong with harlequin rasboras? Worms, breeding?

So, just now I noticed when I got home from work that most of my harlequin rasboras are pretty fat... I didnt notice this before... I also noticed that my rainbow shark is kind of fat too... Recently all four of my tiger barbs and one oto cat died... I honestly do not know why. I have 6 rasboras, 1 juvenile rainbow shark, and one oto cat. I feed them tetra min tropical flakes, peas, wardley algae discs, and once about a week ago, freeze dried blood worms... My rasboras flare their fins and do a dance, but I always thought it was for dominance. They could also be constipated... But I only fed them a few tropical flakes this morning and they don't seem to be swimming too oddly. But my rainbow shark has been swimming around and then pausing a little, and then swimming again. I do have a anubias plant as well. Please tell me if its worms or something else!

 

Specific water parameters please. Is your tank cycled? Size? Other tank mates? Snails or shrimp?(could've brought in worms)
How frequent are feedings and water changes?

If you think it's constipation, I hear peas will help

 

All oftheabove, start with a water change.

 

Your stock is a problem. Your rainbow shark will get very aggressive as he ages. And tiger barbs need to be in groups of 20+ in order to keep other fish with them

 

20 seems high to me. Ive done it with half that.
but the tank size effects all my answers.

 

Yea I would rather be safe than sorry.

 

For as good as test strips go... They aren't always accurate... But heres what theyre saying

Nitrate : 40ppm
Nitrite: .5 ppm
GH: 150 ppm
KH: 40 ppm
PH: 7.2

I have a 29 gallon bowfront.

 

I would recommend using Prime. This is the best water conditioner. Sharks are awesome but grow way to big. He will go after other fish so could be a problem since he has a small area. Return him if you can. Also buy API lquid test. 100% accurate. Strips not so much...

 

Yeah... Strips really aren't that accurate.. And ive had the shark for about two months now, and the shark is okay, he won't get past 6 inches, and he has a pretty big cave area. He only bothers fish that come too close to his cave opening, and occasionally at night... But that was when the tiger barbs were there, and they aren't now. He hasnt bothered any other fish than the TBs. I also plan on doing a REALLY cool aqua scape soon! musserump09

 

Ah, and after a water change, theyre back to normal. I guess it was just constipation

 

yeah the tank seems a tad small for tiger barbs and sharks. It snot really just their size, but they have large spaceneeds for high activity.