Terrible things happening in my tank

[MadameGazelleIsMyHomegirl]

Something bad is happening in my tank and I can’t figure out what. One platy started sitting on the bottom
And looks a bit bent. The White Cloud Mountain minnows have started fighting, previously no violence at all. Then yesterday I discovered them all head down stuck in the plants, looking pale and colourless. When I moved the plants they ‘came back to life’ but are off their food. One also looks bent. My shrimp have been flying round tank too.
Tried increased water changes, aquarium salt, bio boost and crystal clear.
What is going on??? Help!!

Could they be eating each other's eggs from the tank bottom (or teeny offspring, in the case of the platy, as I think they're live bearers)?

Have you tested the water? Have you introduced anything new to the tank, any new fish, food? Are the filters clean, is air pump working? If they are looking bent it may be this

Tuberculosis
If a fish has a bent or curved spine, it is most likely infected with a Gram-positive mycobacteria (Mycobacterium marinum or M. fortuitum). This is commonly referred to as fish tuberculosis, piscine tuberculosis, acid-fast disease or granuloma disease. Tuberculosis is a chronic, progressive disease that may take years to fully develop. Symptoms include lethargy, emaciation, fin and scale loss, exophthalmia (bulging eyes), skin inflammation and ulceration, edema (dropsy), peritonitis (parasite infestation) and nodules in muscles that may cause deformation of the fish. Fish that appear to be most susceptible to fish tuberculosis are gouramis, black mollies, neons, and other tetras, carp and anabantids.

Infected fish should be removed and quarantined immediately for four weeks or more. To prevent this infection, do not overcrowd, and provide good water quality. Remove any fish that appear affected. Some successful treatments have been described using chloramine-B or -T, cyclosporine, doxycycline, ethambutol, ethionamide, isoniazid, kanamycin, minocycline, penicillin, rifampin, streptomycin, sulfonamides and tetracycline. In addition, you might try using streptomycin for the first four days at a dose of 10.6 mg/L (40 mg/gallon). After the streptomycin treatment is completed, feed the affected fish with food that has been treated (soaked in) with rifampin at a rate of 10 milligrams per 100 grams of food for about two months. At the same time, treat the aquarium with isoniazid twice a week at a 10.6 mg/L (40 mg/gallon) dosage for one month. If all fish become infected and eventually die, the entire aquarium should be sterilized using a mild bleach solution and rinsed with liberal amounts of water before adding any new fish.

Do you have a local aquarium supplies shop you could go to for advice?

The only thing I’ve recently added was 4 moss balls. I’ve cleaned the filter weekly, and been testing every few days with strips. Ammonia is at 0. One of my nitrates was slightly raised but not horrific. There are pond snails in the tank and they recently had a population explosion so I culled about 20. I’ve been siphoning the substrate weekly. I use tap water conditioner... no idea why it’s gone pear shaped. The behaviour is the weirdest thing- the minnows hanging head down and motionless in the plants is v odd

Sorry, meant to add, yes I wondered about TB too. Bit worried as I’ve a cut on my finger and have had my hand in the tank

cleaned the filter weekly? What do you mean by that?

Its been a while since your post but wondering how things are now, you would clean the spray bar but not the media except in old tank water to preserve the bacteria.