Old Sand?

[BassTank]

Well sad to say it but I lost 3 Malawi cichlids in a week. This tank has been doin so good I never had a problem with it. Tested for ammonia and nitrites but both are good. The only thing I've done differently is last week I added PFS from my 5 gallon hex that's been sitting in water for about 2 months. That might of been an idiot move.... I didn't even think about cleaning.

I also cleaned out my fx5 that had alot of snails but didn't use anything but water.

Is the old sand the cause of sudden death? Or is there another cause? If need more info to come up with a conclusion. Lmk

[cichlid1409]

sand could be a possibility but i would think that you would see ammonia and nitrates if it was the sand. its always best to rinse old sand before adding to your system to avoid contamination problems.
did you use tank water to clean your filter? if you used tap water it could have hurt your beneficial bacteria. just a couple ideas.

[BassTank]

I used tap water to clean the inside of the canister and layers of foam. The bio material was kept in a separate bucket with tank water. And I also cleaned the foam on the wet dry with tap.

I'm treating this tank with metro, Epsom and feeding everyother day now.