[quote="ChrisM"]Cleaning the filter may have eradicated all of the nitrifying and heterotrophic bacteria which break down ammonia and other waste.Check for ammonia and nitrite,I doubt if nitrate is your problem?

Nitryfing bacteria (Nitrobactors) break down nitrite to nitrate,nitrosifyers break down ammonia to nitrite:

NH3 + O2 + 2e- + 2H+ → NH2OH + H2O or NH2OH + H2O + 1/2 O2 → NO2- +2 H2O + H+

Nitrite to nitrate:

NO2- + 1/2 O2 → NO3-

Ok, enough of the chemical talk. Essentially Chris is right. Filter maintenance is important, more so with messy fish like goldfish.
Always clean in a bucket with aquarium or dechlorinated water.
I think this is probably the issue.
I would rule out temperature fluctiations as the cause of your trouble. If you keep them in a pond outside during the summer you will get them too and the fish don't mind.

just an update to let yous know I done the water test and it came up as 7
good or bad??I noticed today that one of the remaining black moors has some sort of injury on his back.If I can I will post a pic.The fish havent moved much all day,still at the bottom.Is there any way at all I can save the remaining fish??Should I move them out of the tank??Really disappointed this all happened suddenly after having these fish for years to see them the way they are now.I now beleive the new fish I added done the damage

Is that a pH test that came out as 7? That's neutral water and perfectly fine. What is more important in your case is ammonia, nitrite and nitrate in that order since they get progressively less toxic to fish. The picture you posted is a bit out of focus but by the looks of it your fish has a cut of some sort rather than an external infection.

Check your water again but I have a suspicion that your fish don't suffer from ammonia/nitrite or nitrate poisonomg or they would be more likley be at the surface gulping for air.

I would try a dose of eSHA 2000. Great braodband medication

Thanks everyone for all the advice and help,however all my fish died one by one over the past few days,velvet disease was diagnosed and it was too late to save them.I want to get back into keeping tropical fish again and wonder what measures I should take to make sure the tank is free from all parasites.
I will strip it down completely,should I get rid of all the acessories?Pump air stones,oraments stones etc.?And buy new?If not is there a good way of cleaning them?
Thanks

Hi Buffy,

Sorry to hear that you lost all your fish. It's best to have a collection of treatments to hand for some of the more common ailments. Therefore, you're equiped to react quickly if you spot an outbreak. The 12 hours to wait overnight to get to your LFS and pick up a treatment can be the difference between life and death.

It's also a good idea to purchase a small tank and set up as a quarantine/hospital tank. Therefore, any fish needing treatment can be isolated and treated. This avoids treating all your fish when they possibly don't need it. You should be able to set up a quarantine tank (20 litres is fine) for around €40 or less.

Parasites will not last very long without a host, i.e. fish. Therefore, since you've no fish, the parasite will also die off. Just clean everything with warm water and it should be fine - avoid using detergents as any trace is very bad for your fish. However, I would replace airstones and filter media.

Problems like velvet usually stem from water quality issues. Make sure you read between now and setting up your tank and understand the cycling process. A test kit is also a must.

I'm sure you've learned a lot over the last week. Unfortunately, this hobby has a habit of teaching us harsh lessons. We all have stories like this to tell.

Thanks for the advice Ken :wink: I will take on board all the advice you and others have kindly given me and I will get a small tank for quarantine,I will be buying all the test kits and treatments I can get my hands on before I set up my tank again,and of course will go through all the threads here and pick up all the tips before I buy any more fish. I hope to post up pics of my new fish in a few weeks time.
Once again thanks everyone for all the help.
Appreciated :wink: