Since you appear to have good mechanical conditions such as aeration water circulation and multiple filtration plus UV for holding fish, I think your problem is with the source fish. During winter especially the source of your fish may have been holding the FHM for quite a while due to lower daily sales. Their holding conditions may not be as good as yours. This can be very stressful long term for retail fish sellers.
QUESTIONS - How long have these deaths been going on? Were the FHM generally okay earlier in the entire fish holding session?? Deaths just started recently?? And when did deaths start compared to when you started holding the FHM for feeding crappie?
You have no way to know how many fish the source is loosing daily. They may not be truthful. I assume you are getting the FHM always from the same place?? I suspect they are loosing the same percentage as you. Quick dying fish after you receive them and you have handled them carefully is very often due to the quality of the stocker fish which can vary a LOT - my extensive experience.
One way to check the apparent health of a new batch of FHM is put a good number in an aquarium for a short period - observe them for sores, red areas, fungus and relative healthy condition.
As mentioned, increasing the salt concentration may help reduce deaths. Look for another source or wait for their new shipment of FHM.
Last edited by Bill Cody; 01/29/20 11:22 AM.
