nothing obvious there is there, have you got a Q tank you could put the shark in while we get u some help on it
the lemon sounds like whitespot if itd flicking.. can you see any white spots like grains of salt on him?
i would be inclined to do a water change just while you get a few more replies, it could have something to do with the conditioner, dodgy bottles have been known, tho im not sure exactly what effect they have on the fish
TBS sounds like maybe slime diesease, but im not 100% so dont treat for anything as yet till you have a definative answer.. look here, you maybe able to pick something up straight away, to me its seems like more than one problem.. few synptoms that you may recognise there
oops wont let me paste the site name, heres a bit i copied n pasted its from tropical fish centre dot co dot ul
Symptons of illness It could be... Treatment
Your new fish have died - there are no obvious signs of illness "New Tank Syndrome" Adding fish to a brand new aquarium stresses the fish, and sometimes it can be fatal. For more info, check out: The Nitrogen Cycle
Loss of appetite An enviromental problem, newly-introduced fish can be slow to feed (stress), certain fishes will refuse anything but live foods. Enviromental: inspect for any manifestations of disease, and get a basic water tester (Ammonia etc). The same with stress. Be patient with them. Look for other signs of disease.
2,3) Cotton Wool effect on the body Fungus, Columnarius (Mouth fungus) If you see this disease, can use medication (ie "Anti Fungus") and a Salt bath (1 teaspoon per gallon)
1) Small, white spots on the head, body and fins. Whitespot (Ichthyophthirius) A very common disease (especially in a new aquarium). There are several formulas around, dose the fish quickly before the parasite spreads. Salt could be used (1 teaspoon per galloon).
8) Fraying of the soft tissue (fin membrane) Fin Rot, the disintegration of the fins Use medication before a secondary infection occurs, it will take several days before there is serious fin damage. Could use salt bath (1 teaspoon per gallon)
Appearance of a whitish film over the eye of the fish Poor water quality, poisoning (Chlorine) or Eye Fluke Poor water: Water changes are required. Poisoning: Make sure to condition tap water. Eye Fluke: Use medication
4) Fish are gasping, on the bottom of the aquarium, red streaks around gills Most probably oxygen starvation, or a Gill disease You have too many fish, an air punp may help. Gill diseases are quite rare, you could actually see the gills rot away: use medication.
5) Worms are visibly seen hanging from the gills, fish are gasping Gill Worm (Dactylogyrus) This is another parasite. Use anti-parasite drugs as directed.
7) Reddining of the skin, or red streaks in the fins Virus, Ulcers (Bacterial infection) Viruses can only be seen through microscopes - and its incurable. With a bacterial disease, use a anti-bacteria or anti-internal treatment. A prolonged SALT bath (3-5 g/litre for several days) will alliviate osmoregulatory stress in the case of severe ulceration.
Scales seem to be raised, fish are bloated. Dropsy (Ascites) Dropsy is more of a sympton than an actually disease yet, and is quite common. Most associated with a bacterial infection (cause could be wide - poor water conditions are often the culprit. Meds can be used, but dont always work.
Small, worm like parasites attached to fish, fish scraping against rocks. Anchor worm (lernea) There are many Crustacean Parasites around, and can be exported into your water. Meds are available.
6) Dull colour (mucus), detached skin, fraying of the fin. Mucus Hyperproduction. This called by caused by Slime disease (parasite, meds available), poor water conditioners (high Nitrogenous wastes), fFukes, stress.
it could be as simple as the conditioner.. lets hope eh, good luck 
