Slowly loosing fish. Help

[Michael14]

Hi I have a 170 ltr aqua one vogue tank and have
2 angel fish
1 soard tail
3 coarys
4 golden barbs
1 ruby shark
4 tiger barbs
And 2 catfish things lol.

Reason I'm posting is because I am slowly losing my fish 1 every few days all the water test are fine only thing is slightly off is the pH level is slightly low.
Now my angel fish looks like his fin is stuck to his body on his side and has a red mark were his fin meets his body.

I do a partial water change every few daysdas im strugglingsto get the algae under control.

Any help would be grateful

 

[Byron]

We will need data on the water, as "tests are fine" doesn't tell us much. If you have tests for ammonia, nitrite and nitrate, provide test numbers. Also, what is the pH..."slightly low" doesn't tell us. And do you know the GH (general or total hardness) for your source water?

Second, what volume are water changes? What is the temperature?

Can you be more specific about the "catfish things"? We need to know the species.

All of the above can be part of this. But thirdly, you have some serious stocking issues. Tiger Barbs must never be in the same tank as sedate fish like angelfish; this might be the problem with the angelfish. Have you observed any interaction among these fish? Ruby barbs also are not suitable for angelfish. Or one of the angels may be harassing the other...they should never be kept as 2, 3 or even 4. This tank is really not large enough for angelfish aside from the rest.

 

[Cichlids]

Is your tank cycled? If it’s not the water may be unstable