Colu

Looks like possible injury with secondary bacterial infections what I would do a course is of kanaplex and add an extra air stone during treatment @aaron eli

All the symptoms am seeing are associated with low pH and KH without increasing these your no going to see an improvement if you can get some wonder shell that will temporarily add some minerals to your tank Epsom salt will increase your GH it won't increase your KH Which is the more important one what I would do as you have live plant is add 1 table spoon for 5 gallons of Epsom salt I wouldn't go above that level with salt

What I would do is get a GH and KH test kit or the 5in1 test strips when you no your GH and KH then I would add some crushed coral to help raise your GH and KH if it's low typically you want to 1pound of crushed coral for 10 gallons higher temperatures are good when treating ich help and to help encourage a sick fish to except food higher temperatures can increase mortality with epistylis and columnaris and higher temperatures shortens the life of your fish

Could be an issue with there swim bladder could be old age typically x-ray tetras only live 5 years I have some that are 6 year's old that are starting to develop odd swimming patterns they have been doing it for months still eat fine and are active if it were an issue with the swim bladder you would want to do Epsom salt baths 1 table spoon for 1 for no more than 15 minutes for 5 days as Epsom salt acts as a muscle relaxant to help relieve pressure on the swim bladder

No algae has nothing to do with Popeye excess algae is usually caused by excess nutrients or two much light I keep my lights on for 8 HR a day I don't get algae problem I forgot to mention another cause of Popeye is a growth behind the eye this isn't as common as a bacterial infection or injury to the eye if you don't have live plants you can add a higher level of salt 1 table spoon for 2 gallons given the length of time Tue damage might be permanent

Popeye usually caused by a bacterial infection when it effects both eye's when it's effecting one eye it more likely to be caused by an injury given the medication you have used and fact you you haven't seen any improvement would mean your more than likely dealing with an injury to the eye sometimes the damage can be permanent what I would do is is add Indian almond leaves as they have antibacterial and antifungal properties and leave a low dose of salt in the tank 1 table spoon for 5 gallons that will help reduce fluid buildup in the eye for two week

Most of these ingredients are found in aquarium fertilizers I wouldn't replace your tank I would just it leave a couple of days and keep an eye on your water parameters

What are your water parameters ammonia nitrite nitrate pH KH GH shimmying can caused by low KH and GH I would low the temperature to 25 degrees

That an encouraging sign

With the white patches what I would do is a course of maracyn just in case there's a bacterial component add a small amount of aquarium salt 1 table spoon for 5 gallons the salt will add essential electrolytes and aid Gill function add an extra air stone during treatment @Elyse

Possible internal parasites I would treat with expel p once a week for 3 weeks

Has it any rapid breathing hanging near the surface spitting food out sunken belly

You could do a course of medicated food he's a medicated food recipe for levamisole @Stroy15

Just treat this fish on it's if you can't quarantine than I would treat the main tank with ick x

Spitting food out can be a sign of internal parasites what I would do is treat with Fritz expel p once a week for 3

With the symptoms your seeing and how quickly they died once you see symptoms it could be a bacterial infection what I would treat with kanaplex @CiderLovesFish

What are your water parameters can you take a picture of the sick fish @BlueTurtle25

What I would do is treat ick X and do salt baths 1 table spoon for 1 gallon for no more than 15 minutes for 5 days mouth fungus can kill very quickly so start treatment straight away @HelplessNewbie

When did you lose your first fish how long from the start of symptoms before they died have used any medication if so did you see any improvement after treatment

Any rapid breathing hanging near the surface lethargy flashing erratic swimming spitting food out @Stroy15

I think there are sold under multiple different names depending on were there sold in the UK I think have seen them for sale as albino long time ago

I think there sold as albino neon tetras

L Good to hear he's made a full recovery

If you don't have live plants I would dose the tank with salt I would never add methylene blue to your tank it will kill your beneficial bacteria

I would only use a 5 gallon tank as a shrimp or snail tank 10 gallons is the minimum i would do if you want to add fish