black moor died

Question
hi , i recently (1 month ago)introduced a black moor to my aquarium. i quarantined it for 2 weeks before adding to the aquarium but after 3 weeks of all being well it became very ill and died suddenly( within 24 hours of displaying symptoms of illness). its fins clamped and it started to change from black velvet to light gold metallic all over apart from its fins and eyes.it just sat on the bottom of the tank but came up for feeding. it showed no signs of swim bladder or bloating and swam well until it passed away(no side swimming etc)i tested the water as soon as i noticed its fins clamped and all was spot on. the other fish in the tank (2 gold fantails 6 white cloud minnows and a jap weather loach) have all been fine. the tank is a 54(uk)gallon tank which has been established for 8 months.  am a bit concerned the black moore may have had some sort of disease? should i treat my tank increase water changes to daily instead of every 3 days? i hope you might be able to shed some light on the matter and offer me some advice.
ps there are no live plants in the tank . it has an interpet pf4 filter and air pump. small amount of gravel plenty of hiding places

Answer
Hi Julie,

What you describe sounds like your black moor died from a disease commonly called velvet. To make sure, do a Google search on the words:
oodinium
velvet fish

Here is a high resolution (and very large) image of a clown loach with velvet. Is this what your black moor looked like when it got sick?
http://www.fishdeals.com/fish_diseases/oodinium_velvet/photos/velvet.jpg

Velvet leaves a fish looking "dusted"...it's really the only disease I know of that will rapidly change the appearance of your fish as you describe. Do a bit of research to see if my suspicions are correct.

If you agree, then have a look at the website below:
http://www.wetwebmedia.com/FWsubwebindex/fwfishmeds.htm
Velvet is the second to last entry on the chart that suggests medications based on disease. Since Neale Monks is a UK aquarist, he suggests many medications available abroad and a few here in the US.

Do test the water parameters, to be sure there's 0 ppm of ammonia and nitrite. Your tank is ample for what you are keeping, so provided your filter provides sufficient turnover and you are feeding a diet not too rich in protein, I don't suspect you will have a problem with either of these levels...but do test to make sure. Here in the US, the golden rule about nitrates is that they ought to be <20 ppm in freshwater tanks - however <50 ppm is safe.

A water change wouldn't hurt and might help, as might running carbon to absorb as many organics as possible before you medicate, if you choose to do so. Velvet will need prompt attention, if it is indeed the case. I rather hope that I am mistaken, because this disease can be persistent and difficult to eradicate...at least compared to things like whitespot. It's hard to blame such a sudden death on genetics, however I know that black moors have been known to change color. (Google black moor color change to see lots of results.)

Nevertheless, it might be worth a try to ask the retailer you bought this fish from if he has had any trouble with his fancy goldfish.

I wish I knew what else to suggest, this is an out of the ordinary situation! You seem like a conscientious fishkeeper who was stocked their tank very sensibly. Perhaps you should check out this:
http://www.wetwebmedia.com/FWsubwebindex/fwdistrbshtart.htm
Which is a page on disease troubleshooting by Neale Monks again.

I hope that helps, take care.
Nicole