I just setup a hospital tank to treat ick with hyposalinity. I'm worried about lack of biofiltration. I want ro throw some of my DT's rock in therento help. Iwill rock still help filter in hyposalinity?
You should be worried about the lack of nitrification in QT, but in general you should not put mature LR into QT. Either hypo or copper will kill many inverts lives on the LR and polute the water in QT. Exception is when the LR is still rather new but is just cycled; and even then if you used copper it will deposit on the LR.
Hypo gradually achieved or copper should not have a major impact on nitrification bacteria.
The lesson is that one should QT in advance and plan and cycle the medium intended for QT in advance.
The medium for QT should be cycled very well in advance. Use the seed and waste method and not any gradual method to cycle.
If you do not QT and wait for ick to attack when you are not prepared, you will be in a bad situation, as you are now in.
If you cycle now in a separate container the medium intended to be transferred to QT , you may need to change water in QT for only about three weeks after the cycle is done, not eight weeks.
BTW, LR is not a good medium of filtration in QT. In QT, you don't need denitrification or other comprehensive microbial balance, just nitrification. LR is too bulky in QT, IMO.