Changing Substrate With Established/Started Tank?

Any tips on changing substrate on a tank that’s already set up? I’d like to eventually change the sand from white to black, but don’t want to completely throw off the balance... Picture of tank in question.

SnuggleBug’sMama said:

Any tips on changing substrate on a tank that’s already set up? I’d like to eventually change the sand from white to black, but don’t want to completely throw off the balance... Picture of tank in question.View attachment 115789

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I'm doing the same thing myself.
What I did was to make a wall (of sorts) a third of the way along from one end. I then removed all the sand and replaced it with the new substrate. I'll be changing another third (the middle section, in another week then doing the other end of the tank a fortnight after.
I must admit that the black substrate is way better too. I'm using some at 2mm - 4mm so the corys don't have problems with sorting through it.

@HoldenOn just changed his tank's substrate so might have good tips

If there's fish in there you're better off moving them to a bucket for the duration, keep an airstone in with them at least.
Depending on your filter type, if internal, try and move this into the bucket. If the flow is too powerful, just leave it switched off but keep and airstone under it. If cannister, then just keep off throughout.
With sand you can actually suck it out with a syphon, the tube would need to be a good diameter, such as a garden hose. Once removed and the water removed (as much as possible) you can pour in the (washed) new sand.
Keep an eye on water parameters after as you will have removed some bacteria that lived in the substrate. Any readings of ammonia or nitrite would prompt for a 70% water change.