goldfish nightmare

 Am fed up with the goldfish situation in home had one goldfish in the tank a yellow comet which had for about a year but recently it diedtoswim bladder and thinkng about it so have alot of the other goldfish had to, especially the orandas and fan tails.

  So brought a mixed coloured comet small thing and a gold coloured one, the gold coloured one again seemed to have early stages of swim bladder after about a month didnt get it from pet shop tank and it eventually died.

  Got this mixed coloured comet which seems fine but am scared to put any more in in case damn swim bladder gets them brought the medicine but it does nothing its such a fatal diesese.

  Why do they get it is it feeding flakes etc oxygen intake to much or is it just bad luck the tank is clean nitrates and ammonia and the ph is alkaline over 8 which assume is ok for them.

  When they get white spot its quite easy to cure but this swim bladder is lethal. 

  Tried salt and boiled peas which theydont go for so what should do now then?

 Also just like to add that when sort this issue out have a plec from tropicals that want to putin coldwater tank wll it be ok in there going from two different temperatue zones.

  Its to clean tank had sucking loaches but they chase like mad

I reckon pellet foods are better for fancy goldfish than flakes.  I actually heard that flakes can cause buoyancy problems in some varieties.

Do you change the water fully?  This isn't a good idea as it removes useful bacteria.

Do you treat the water before putting it in the aquarium to remove chlorine?

Is your filter adequate for the size of the tank?  In the case of goldfish it's not a bad idea to get a slightly larger one than recommended due to the amount of waste they produce.

If you don't think it's any of the above then you may be using a dud stockist.  It's best to go to a specialist aquarium store where the fish seem happy and healthy. 

as asked, how big is the tank? Whitespot is normally due to stress whether it be caused by your tank or the lfs's so something definatley isn't right. 

If the fish stocking is ok for the tank size and you do weekly gravel cleansand water changes of approx 20-25% then there shouldn't be a problem in theory.

Hongkong plecs or Panda Garra's will be ok for algae cleaning depending on tank specs/stocking levels.

Could you post some water test results along with some specifications of your tank please for us to be able to help better