Some shops (not mentioning any names) will advise stocking in excess of 1cm per litre, which is over double a sensible stock for a tank with normal filtration. Some people can significantly bend the inch-per-gallon rule (which is a pretty rough guide) but only in certain cases, with certain filtration and certain species of fish. LFS want to sell you fish and are not looking for an arguement in the middle of the store - they are very unlikely to tell you that your stock is way out, even if they know it is (which is often doubtful).
Overstocked tanks and inadequate shoal sizes cause stress, which in turn causes weak immune systems, which lets diseases take hold. It's always a really bad idea to do risky things on the basis that "it's been OK so far", because it often takes one tiny thing to make it not OK, and often when it's stops being OK, it goes wrong in a BIG way.
White "saddles" sounds like columnaris to me. Can you get a photo? If it is that, you need to treat with anti-bacterial meds. Wilder can advise on specifics, as I've never had success with treating this nasty disease. I do know that lowering the temp as far as is safe for the fish (so maybe to around 24 C) and doing very frequent water changes will help.
If untreated columnaris will happily wipe out all of your fish. I really hope it is a mild strain or isn't that at all.
3 zebra danios - need groups of 6+
10 neons - fine
7 glowlight danios - fine
4 rummy nose - need groups of 6+
5 clown loach - need 6 foot long tanks
1 shark - what kind? Rainbow and red-tailed need 4 foot/200+ litre tanks, bala/silver sharks need groups of 3+ and 6+ foot tanks
5 black phantom tet - add another buddy ideally
5 bleeding heart tet - ditto
2 tiger barb - need groups of 6+. Nippy, aggressive fish that will stress others if in small groups
1 green tiger barb - ditto
3 peppered cory - OKish. Ideally 6+
2 bolivian ram - fine
2 krib - pair? Could be OK. Watch out for aggression when breeding
5 black neon tet - add another buddy ideally
5 cardinals - ditto
2 bristlenose catfish - fine
1 clown plec - fine
At the moment you have 191 inches of adult fish (i.e. if all your fish hit a decent average for adults that's how much fish you'll have). If you remove the big ones (clown loaches and shark), you'll have 123 inches . . . so you'd still be looking at a 100 gallon tank as a minimum. That's 450 odd litres. If you add all the right fish to bring the groups up to minimums, you're looking at 169 inches or 150+ gallons. With excellent filtration (so a filter that could handle a 180-200 gallon tank, you might be able to get away with 130 gallons . . . these are just rough workings by the way, but at least it gives you an idea.
To keep things safe and for you not to have to upgrade your tank very soon, you're looking at cutting down to about 40 inches of fish (as a maximum). So that would be (for example): your kribs, your neons, a bristlenose and a shoal of 6-10 black neons/cardinals/rummy nose/other tetras. Not many fish.
Obviously, if you do get a 6 foot, 150-200 gallon tank with excellent filtration you could keep most of your stock.
As always, sorry to bring bad news. We only have the interests of your fish at heart.
