Rainbowfish Constipation

Yes, definitely best to treat in the spare tank. If you can cut / take out a small portion of the filter media from the main tank's filter and put it into the spare tank's filter (whatever fraction would correspond to the two tetras' body mass relative to the other fish), that ought to be sufficient to process the two tetras' waste.

He seems better today, he is at normal position in the tank, doesnt seem as active as he normally is though, hopefully will improve in a couple more days. Im holding off feeding for today, and gonna throw away the freeze dried bloodworms just incase that was part of the cause. I bought a frozen tropical mix from the fish shop yesterday anyway so will give that a try for a treat once a week instead

I have put the two tetras in a seperate tank and treating with esha2000 double dose yesterday, couple more days maybe i will see some improvement, they look all lonley in a 39L tank on their own lol.

Thankyou for all your responses, i am learning more and more each day about these fish! I seem to have been quite unlucky in some ways so far :-/ which brings me onto something else that has been bothering me about one of my female rainbows....

Shortly after i bought her i noticed she had something differerent 'inside' her to the other females, she acts totally normal and seems happy etc but im wondering what it is. Almost looks like a lump on the inside or something, the outside of her scales are unaffected. Pics attached, i circled the area its in, not so easy to see in pics i guess. (Pretty funny snap of her with her mouth open next to a tetra too lol)

Just to update stumpy the constipated fish is back to his normal self Thankyou for all your help!

I have thrown away the freeze dried blood worms...and after seeing the difference in the blood worms that come in the frozen food I am glad the freeze dried ones are gone as they looked nothing like what's in the proper frozen cubes!!