I have an unwell small Black/Grey Fantail at my work after being overfed over easter break, and tank dirty, one Pet store gave me Melafix which helped a little ( he has blood red marks around gills),  but my regular pet store thought might be septasemia (sp) so gave antibiotics,  a big improvement has been shown and he is now swimming around and looking for food. 
 
Only problem is he seems to be nose down and bum quite a bit,  almost like he has lead in his head and air in his tail and he cant keep level. 
 
I have read up on bladder problems but doesnt fit the discription given. 
 
Water is now fine , and have followed all instructions given by pet store,  am wondering if trying a pea ( suggested on several websites for bladder issues) and maybe some salt ( the aquarium stuff) any other suggestions or advice. 
 
He is much loved by the staff ,  his name is Pepsi,  and his friend Mirinda (tiny orange gold fish) keeps him company ,  we recently retired Coke and Fanta to my pond as they got too big for tank  .   
 Thanks in advance for your advise.