I have never kept those, I kept J. ornatus and J. regani (on separate occasions) both bred but it was nothing to do with me, I just noticed the fry one day darting out from the rockwork picking up small fragments of food. Mine were very secretive but very interesting too.

http://www.youtube.com/watch?v=RS2Hnw7N3Fk

I used to breed both N. multipunctatus and L. ocelatus.
I kept just a pair of N. multipunctatus in a 2ft tank and covered the floor with shells and the colony built up to around 50 individuals (arrrgh in a 2ft tank) but never above this number despite still breeding.
They kept me in fish food and other bits and bobs through exchanging them at my lfs.

Great little fish.

There are two causes for this condition and they aren't related even though the symptoms are identical.

1, Dietary, gas becomes trapped in the fish's gut and makes the fish buoyant the causes are many - gulping in air with the food when feeding at the surface, a diet which is to low in fibre, the fish are fed to infrequently and so on.
This condition is easily fixed by feeding small amounts often, pre soaking food or using non-floating food, using fresh greens, raising the temp a little (18 - 22C) and by using epsom salt at 1 level teaspoon per 4 gall for really stubborn cases.

2, Genuine swim bladder problems, fancy goldfish are prone to problems with their swim bladders more than other fish due to their body shape, the swim bladder is a paired organ in carps and sometimes one side can remain under developed or the whole bladder can be in the wrong place. A young fish may even appear fine but as it grows and develops the problems also begin to develop. This is a physiological problem and CANNOT be treated with potions of any sort. Only surgery could correct this type of problem and that is out of the question in almost all cases (I have heard about this being done successfully on a large and very expensive koi). Disease is often cited as a cause but unless the fish is showing symptoms of a disease it is a most unlikely cause.
The swim bladder is controlled by muscles which allow the fish to expand or compress the bladder and in fancy goldfish these muscles are generally quite weak when compared to standard fish of a similar size. If they are forced in to using these muscles due to being kept in deep water it can lead to this sort of problem and this is treatable.
Keep the fish in water which is very shallow (enough to cover the fish with an inch or so to spare. This will allow the muscle time to heal and the fish return to good health, but this is only in a tiny minority of cases.

Having read the entire thread I noticed that this has gone on for a month now and so it only seems sensible to rule out a digestive problem after this long has passed. If air was trapped in the gut so would partially digested food be and this would begin to rot and almost certainly kill the fish by now.

I would forget adding a myriad of chemicals to the water and simply raise the temp a little to promote healing and try the fish in very shallow water for a few day.

If there is no improvement then other things will have to be considered because a month upside down, unable to feed properly and possibly with some discomfort and certainly very stressed - isn't really much of a life.

I haven't used it myself but others have recommended this:

http://www.warehouse-aquatics.co.uk/w ... r-sticky-stuff-290ml.html

"Cone shaped dandelion"

Those sound a lot like christmas tree worms. Search google images and see if it is those.

The pH seems quite low and this suggests that insufficient water changes are being made, I'd expect it to be nearer to 8.2 - 8.4, you will probably need to take this up with the guy who is maintaining the tank for you.

If the fish are being fed with dry food alone then I'm even more convinced that this could be the cause for the losses. There is a large range of frozen food for marine fish (probably the same stuff you use for the anemone) most places which sell the fish sell it, the range will include a diet for herbivorous fish too, this would be much better for the fish in the long run.

The white daisy looking plants which 'indicate good water quality' sound interesting because the only marine flowering plant I know of is sea grass, is it an actual plant or some type of coral/anemone?

Over all so far:

1, Better live stock selection, there are plenty of colourful and interesting fish available which are more forgiving the odd mistake and are more suitable for novice fish keepers. There are many care sheets online which will advise about this.

2, Improved diet for the fish to include more frozen food rather than dry food.

3, More water changes so that the carbonate level is boosted and the pH brought up a little.

Finally, marine fish can be challenging but they don't just die without good reason. Having someone come in to look after the tank (presumably a paid for service) to make a statement like that smacks of a can't really be bothered attitude and that seems very poor.
I'm glad that you posted here and I hope some that some of this will help. But do check back later because someone with more experience than me with marine fish may be able to offer more helpful advice.

Andy

When you say all the water perimeters are fine it is better to put the actual water test results, no disrespect intended but what some people call fine is sometimes anything but.

There is nothing which really looks like an outstanding problem with your tank written in your message but quite clearly there has been a problem with some of these fish. One thing which does catch my eye is to do with the species which have failed to thrive in that they all require specialised diets.

Blue cheeked gobies, Valenciennea strigata get the majority of their food by sifting the sand for copepods and larger "dead" food could be refused. Once the copepod population has been depleted the fish may eventually starve or become weakened to a point where it succumbs to an opportunistic disease/predator/bully ect.

The Algae blenny and Yellow tang are both herbivores and need to graze almost constantly on fresh greens or food like nori. If they are fed once or twice daily with mainly meaty food both species could possibly go in to a slow decline.

There are of course many other potential problems which could be a cause of the deaths but going off what you have said the above is what immediately springs to mind.

More details may help to pinpoint a more likely cause:
The actual water test results
Food and feeding regime.
Any odd symptoms, marks ect on the fish before they died.
Is this a fish only tank or a reef system, is there any live rock in the tank.
Filtration/water movement.

The more that is known about the tank the more likely someone here will be able to help.

Best wishes
Andy

Nitrite (NO2) is very high at O.5mg/l, ideally it should be undetectable, at 0.5mg/l it is potentially very dangerous to the fish, you will need to keep making water changes to lower it and keep it low.

Carbonates are very low too at just 40mg/l (KH2.2) this really should be doubled at the very least or there is a danger that the pH may crash. You can raise the carbonates by adding bicarbonate of soda to a small volume of water and letting it dissolve then add it to the tank.
3 grammes per 100 litres will raise the KH by 1

Fungus in the mouth area could well be columnaris (mouth fungus) which is so called because of how it looks, but it is actually a bacterial disease which can't be treated with a fungal remedy. The best option is to use a treatment which treats both bacterial and fungal infections. Adding some salt at 3 grammes per litre would be most helpful too.