Move all fish, plants, shrimp to a separate container. Using the old water is optional.
Run the filter on that container.
Redo the tank.
Add some nitrifying bacteria if you think you need to. If the tank is densely planted (so many plants you cannot see the back wall) then I would not bother with the bacteria. However, if you are also doing a major plant trim I would add a bottled product that includes Nitrospira species of bacteria.
Run the filter on that container.
Redo the tank.
Add some nitrifying bacteria if you think you need to. If the tank is densely planted (so many plants you cannot see the back wall) then I would not bother with the bacteria. However, if you are also doing a major plant trim I would add a bottled product that includes Nitrospira species of bacteria.