Substrate change

[Phil R]

Hi, I am thinking of changing from sand to black quartz gravel similar to Dennerle black quartz. I realise this is a major undertaking in a Rio 450. I've done a lot of reading and most people recommend taking fish and decor out but they are changing much smaller tanks. Is it possible to just do say quarter of the tank at a time and leave fish in. I don't have anywhere to put that many fish (nearly 60) if they have to come out. I'm thinking to clear quarter to a third of the tank of sand and plants then add gravel with a separator to keep sand and gravel apart. Do this once a week at water change until all sand has been replaced. My local LFS sells the black quartz but not Dennerle. The grain size is the same and edges are rounded as in picture below
Has anyone done a change by doing it this way and were there any problems both during or after?  Any comments welcome. Thanks.

Phil.

[plankton]

Do you have fish with barbels?
If so, rub that between your fingers. It may not look rough, but it could be, the only way you'll tell is by doing that and seeing if there's any scratching.
The method you're looking at should be ok. Make sure the separator doesn't have sharp edges, and also make sure you wash the sand well before putting it in, otherwise you'll get a very cloudy tank.

[Phil R]

Thanks Ian, yes have corys and loaches so will go to the LFS and try the between finger test. I will also check with them to see if it is suitable.

Phil.