Hillstream loach pale and paralyzed

[Howfie_03]

I had 6 hillstream loaches in a 40 breeder with a school of neons and a few guppies and a female betta. Yesterday I found a hillstream upside down, extremely pale and gasping and aside from gill movement appeared to be unable to move its body. I moved it to a hospital tank but it was dead in 15 minutes. Today it’s happening again. One more is extremely pale (pic attached, can’t move its body). I expect it to die soon. 
 

water parameters:

77f

0/0/20 ammonia/nitrite/nitrate

7.6ph

250 ppm GH

120 ppm KH

0 chlorine/Chloramine

 

No signs of ich, or fuzz of any kind on any fish. The other 4 hillstreams are zooming around eating baby brine (but so was this one yesterday). All other fish seem normal. No new additions to the tank. I did a 20% water change just now. 
 

what should I do? Dose bacterial meds? Do the trio? Just wait and see if any others show symptoms? So far just 2 hillstreams so maybe something specific to that breed? Idk. Help! 

[Colu]

How long have you had them  are they eating ok do have an airstone for extra airation 

[Howfie_03]

On 12/2/2021 at 8:24 PM, Colu said:

How long have you had them  are they eating ok do have an airstone for extra airation 

I’ve had them about 6 months ish, they usually eat great - they love blood worms, brine shrimp and spiralina flake- and yes I run a tidal 55 on one end of the tank and a sponge filter with an air stone in it on the other end. 

[Colu]

 Loss of colour and rapid deaths can be a sign of Columnaris but am not sure that what's happening here have you added anything new to the tank resently @Howfie_03