Question on changing gravel with established bacteria to cichlid sand. My 36 gallon bow with 8 adults and 7 juveniles recently went under a huge cleaning due to 6 weeks of deferred maintenance and tons of glass and rock surface algae. My Eheim 2217 was also down to a trickle so impeller was pulled and cleaned. Now in tip top shape (see pic below) and ready to put rocks back in and my new 3D background.
First, seems like a good time to change out my 3 year old black grand to cichlid sand. My biggest fear is that this is where most of the beneficial bacteria live (aside from filter). The filter media was also thoroughly rinsed so possibly some bacteria lost in that process.
1) Can the gravel be changed/replaced without losing all the beneficial bacteria?
2) Can I add sand with the tank already filled with water?
3) Any reasons for or against the sand vs existing gravel?