This sounds strange. Can you get a few pics of different groups in the tank?
What are all the parameters,
GH,
kH,
TDS? Temp?
Any thing - changes, like moved the tank, changed media, foods, ferts, light schedule, temp of tank? Water change schedule difference?
Plants, moss, new shrimp, fish, snails?
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New to FW fish? First tank in a long time or EVER??? Need some info on keeping fish?

Start here - Aquarium Advice Article
https://www.aquariumadvice.com/guide...ater-aquarium/
FW Favorites right now Clown Loaches, any shrimp - SW Vase Red Mangroves