one fish has been sitting quite still on bottom with mouth opening and closing,sometimes shaking its head, and sometimes gulping big yawn like gulps like 3 a second.
now a second fish seems to be doing it.
one is fine.
been reading symptoms on net,could it be flukes?

Given the recent history of your tank and the lack of reliable water stats, it's more likely that the water is the problem. Have you got a decent pH test yet? What are your current results for the tank for ammonia, nitrite, nitrate, pH and gH?

EDIT: Are you treating for ich too - I seem to recall you posted that they had ich the other day?

I can only agree with FL at the mo, sounds like water quality to me too If you can test everything and report back hopefully things will be clearer

i bought api yest only to find it only went to 7 on card so had to order a high range 1 off net.
ok i'll have to wait until i can post results.
should be here tomorrow

Post the rest of the results anyway - it may not be pH that's the problem. If it's somehing else we can advise on what to do tonight and start sorting it out faster.

no, not treating for anything at the mo.
just 1 of the fish i've had for ages was flashing and bottom sitting and gulping thought i could see grains of salt and it's never done that before until i got the new fish.
just thought it had caught something.
will post results as soon as can.
thx

ammonia 0
nitrite 0
nitrate 10
gh 80

It could well still be the low gH to be honest. That does need resolving by adding minerals to the water but the change needs to be gradual as we discussed.

I think the simplest way for you to achieve it is to use a commercial remineraliser. Seachem Equilibrium (powder) or Replenish (liquid) are both good and have clear dosage instructions. For goldfish I think Replenish may be better as the tank won't be heavily planted. It's easier to dose too.

Post the pH when the High Range test comes, but if you're at the limit on the low range test, then unless it shows a ridiculously high level, that won't be a problem.

i have Seachem Equilibrium on order arriving tomorrow.
there's something definately not right...
my 3rd fish has just darted round the tank like mad smashing it's head into the gravel. exactly what the 1st done whithout the darting.
i've had these fish over 6 months and never done this???
why are you so sure its water and not disease?
i would think that if my fish were fine then stock that died whithin 12 hours and had clear signs of disease where added then suddenly all 3 of mine were behaving erratically then i would be 99% sure that it would be disease of some sort?

There are a few reasons.

Firstly, your fish show no specific disease related symptoms, but the symptoms they do show are classic for water quality issues.

Secondly, your fish haven't been fine, you've already lost one. They were probably bought locally? If so they were used to the water and it's taken time to affect them. The fish from Star were suddenly moved form one set of conditions to another which was radically different.

Your water readings have been all over the place since before the tank was cycled and it's a newly cycled tank which won't have helped.

Low gH is known to be a problem for goldfish - and symptoms of gulping, bottom sitting and flashing are typical.

Star's fish died with a day of arriving; too fast for any disease and you didn't mention any problems when they arrived. The pics were commented on by many of us as to how good they looked.

Star would be aware of any disease problem at their end, but they don't seemt to have a problem. They would not send sick fish out as they have a very good reputation to uphold.

Finally, in most cases, any actual illness in fish (particularly pasasites or similar) is a manifestation in the main of fish with compromised immunity due to water quality issues.

As we're very clear that your gH is too low that will be compromising your fishes' health. Trying to medicate on a guesswork basis where there is no clear symptomology to guide you to the right meds may only make things worse.

Sorting the water out may well be a cure in itself, but if not, the fish will be better placed to recover from any infection if the water is right.