Need help fish keep dying

[orionxtr]

Hi my fish keep dying for no reason roseline sharks 3 of them and 4 plecos I have not added any fish in a year do 50 percent water change a week I have a uv sterilizer should I put it on the tank ?

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[Oddball]

Water test results? Temperature? Matched temp or cold-water replacement at water changes? Are aerosols used frequently in the house? Insecticides, easy-off on warm ovens, furniture polish, etc? Aquarium decoration materials? pH swing on water change?

Need lots more info.

 

[xraycer]

Hi my fish keep dying for no reason roseline sharks 3 of them and 4 plecos I have not added any fish in a year do 50 percent water change a week I have a uv sterilizer should I put it on the tank ?

Sent from my HTCONE using MonsterAquariaNetwork App

Water test results? Temperature? Matched temp or cold-water replacement at water changes? Are aerosols used frequently in the house? Insecticides, easy-off on warm ovens, furniture polish, etc? Aquarium decoration materials? pH swing on water change?

Need lots more info.

There is a reason why your fish are dying, you just need to figure out what it is. Something has changed or there's something that's been killing them very slowly. As Oddball posts, need a lot more info starting with water parameters and chemicals used around the home.