the fiber should not be a problem. But what could be the problem is alot of potted plants come from farms that use heavy ferts (some contain copper) and heavy pesticides. Where did you get the plants from?
well that was before but then i wouldnt do as big as water changes )over 50%) and none died off...If you are losing shrimp everytime you do water changes I think it would be time to start testing your tap water or start using RO.