What should I do?

[joeyr188]

So the substrate in my tank was black gravel sort of and I wanted to add sand so I put it on top of it but every time I do a cleaning the rock appear back at the top the only reason I’m asking is because the gravel has been in there since the tank has been built and I just added the sand 6 weeks ago will it change anything in terms of beneficial bacteria if I remove the gravel but keep the sand?. Also sorry for the poor explanation I do not not how to explain what I mean

 

[Bluebubbles]

Removing any amount of gravel will also mean removing some bacteria however it shouldn't be enough to affect your tank's cycle (assuming it is cycled). While lots of beneficial bacteria grow in the substrate the majority will be located throughout your filter media. Just continue to test your water parameters once you remove the gravel. Adding some quick start to your tank may also be beneficial.

 

[sharkweek178]

When I swapped out gravel for sand in an active tank, I did it one quarter of the gravel at a time. I would take out one quarter of the gravel, replace it with sand, and leave some of the old gravel behind in a mesh bag. I waited a week so that the bacteria could reproduce and repeated the process until I got all the gravel out.

 

[Byron]

I have changed the entire substrate many times. It is always best to do it at one go. Less stress on you as well as the fish. Move them to a temporary tank, and remove all the substrate--I do not know how you would ever be able to remove just the gravel, so toss all of it. A very inexpensive substrate is quality play sand, one bag will do all but the largest of tanks, for 6 or 7 dollars. Home Depot and Lowe's carry Quikrete Play Sand, it is an excellent substrate and completely safe for all fish, something no gravel can claim.

Mixing substrates never works for visual or practical reasons. The smaller grain sand will always end up on the bottom with the larger-grain gravel on top.