Angelfish red line on fin and white patch on top fin

Hello, I am new to this forum. I don't know if I'm posting in the right place but I am worrying about our Angelfish.

Basically we have a family tank. It was set up a few weeks ago and we were given 2 angel fish from a friend that looked happy and healthy.

We have checked the water quality daily and all the points are in the safe area such as ammonia, pH, nitrate. Its all where the test kit says it should be.
We bought some fish from a nearby shop but we noticed that in one of the tanks there was gobys that were dead and the day after 1 of the fishes we bought from the store died, the day after another fish died, so we went back and they said it was a bacterial infection from their store and they supplied us with a bacterial solution to add to the tank to clear it up. They tested our water many days in a row and said it was all perfect and nothing we are doing wrong. Few days later noticed that one gourami in particular was being picked on by 2 mollies, and they were actually terrorising everyone and nipping so we took them back to the shop but sadly the gourami passed away the next day, it was like the fish wasn't able to float properly and was struggling to swim but all the other fishes were fine.

Its been about a week since then and now I've noticed a red line on the side fin of my angel fish, as well as a white patch on its top fin. I tested the water every single day since I've had them and all the markers are in the good range, as well as the fish shop testing the water for everything saying its all good and no ammonia etc.
I really love this fish and I don't want it to be sick or die. I read about fin rot and I'm unsure if that is what the white stuff is on its top fin id be grateful if someone can identify it for me ill attach a picture, aswell as the red line on the fin - I read about septicemia and I'm really worried now.

Apart from the visible marks on the angel fish as described above all the fishes seem happy and eating well.

Please can anybody help because I don't want this fish to die aswell.

Thanks in advance sorry for the long post.

Hi and welcome to the forum

The white patches on the dorsal (top) fin and the pectoral (side) fin are most likely fungus that has infected the damaged fins. The fins can be damaged by poor water quality, rough handling or being damaged on something in the tank (being bitten by another fish, etc).

Check the water temperature and make sure it is 26C (79F) and use a broad spectrum medication from the pet shop to treat for fungus, bacteria and protozoan infections.

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To work out the volume of water in the tank:
measure length x width x height in cm.
divide by 1000.
= volume in litres.
When you measure the height, measure from the top of the substrate to the top of the water level.

There is a calculator/ converter in the "How To Tips" at the top of this page that will let you convert litres to gallons if you need it.

Remove carbon from the filter before treating or it will absorb the medication and stop it working.

Wipe the inside of the glass down, do a 75% water change and complete gravel clean. And clean the filter before treating. Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

Increase surface turbulence/ aeration when using medications because they reduce the dissolved oxygen in the water.

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If you have scaleless fish in the tank (catfish, loaches, eels) then get a medication that is suitable for scaleless fish. If you can't find a medication for catfish and eels then use a normal fish medication at half strength.