What Caused Fishy Deaths?

[AdAndrews]

I have a tropical aquarium 54 litre, with the following fish

2 bosemani(1.5inch)
2 platies(.75inch)
2 otto
2 harlequins


this is what is left from last week where i had fish dying all over the place, all stats are fine, the water quality is near perfect, i even did a 20% change but it didnt help, i have lost overall 3 platies, 6 harlequins, 1 opaline gourami, 1 clown loach, all in this week!, i have been treating the most common disease which was ulcers with melaxzin, but then some of the harlequins developed white fluffy fungus. I am trying to find the cause of this, the day before i had brought some harlequins and brine shrimp, i am wondering if the brine shrimp were off, and caused the fish to gain internal parisites by eating them, or if adding 3 more harlequins introduced serious bacterial infections.
I have realised that the deaths have been caused by either serious bacterial infections that i caught too late in the stages of the disease or internal parisites.

what do you think and what would you advise to do next?

 

[AdAndrews]

bumpeeeee

 

[Colin_T]

not sure what melaxzin is???

if the brineshrimp was alive then it would have been fine for the fish. If it was black and dead then it could have been an issue. However, I would say the new Harlequins brought something in with them.

Ulcers are normally caused by bacteria, dirty tanks and stressed out fish. If the tank isn't cleaned regularly the bad organisms build up and the fish get weaker. Then a point is reached where the fish's immune system is unable to deal with the bugs in the water and they get sick.

Waterlife Protozin or Myxazin will treat most bacteria and fungal infections.

 

[vinylman]

I wouldn't replace the Clown Loach, not in a 54l. What type of Rainbows do you have? Some can get to 4-5''.

 

[Colin_T]

the rainbows are young Melanotaenia boesemani