switching out substrate

[baconbits]

I want to switch out the substrate in my sump. Right now it is 2"crushed oyster shell with 2" live sand on top. (don't ask) I want to replace with all live sand an LR rubble. Considering that I have LR in the main tank al well as CC sustrate that is sure to have some bacteria, would it be ok to just change out the entire sump at once?

[Poseidon]

Any time you remove substrate you are removing some bacteria. I would do it in increments myself. maybe 1/3 at a time. Make sure to test for NH3 and NO2 after you remove the first third, but BEFORE you remove the second third. If there is any NH3 or NO2 wait before removing any more. I would guess a week between each removal should be fine.

A good way to do it is divide the area into thirds using plexi. just shove a piece vertically through the gravel till it hits bottom, then use a SHOP VAC to take out the gravel, leave the plexi in place, put in the sand etc....