help choosing right type and grit of sand pls.

Good news, found local sand! Looking for advice on type and grit (not sure if grit is correct term?). It will go in a 300g 8'x2'x31" tank with a large sump. Fish will be african peacocks and haps. I will also have rockwork.

I found silica sand that comes in 20/30 and 70 grit. The 70 is quite powdery and is nice and white. The 20/30 has more off white and abit of tan in it. I prefer the 70 but concerned it is too fine. I would be happy if I could even gravel vac the substrate rather than trying to siphon just above the surface.
Silica bag:

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All three products compared:

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I also came across sand nickel slag. Is this sandblasting sand? It at first appears black but has abit of a greenish tinge to it. Not sure what this is, I know some use sandblasting sand. I'm undecided on white or black. Right now just happy I found it. Grits are 16/36, 20/50, 30/50.
Slag bag:

Grits:

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Any and all advice and comments appreciated.
Thanks

joe jaskot said:

The way african cichlids dig, you don't want sand that is too fine. Also be sure to put a prefilter on your filter intakes to prevent the fish from spitting the sand into your intake.

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I plan on only running a sump so the water will pass through several layers of matt before reaching anything mechanical (ie return pump). Hope that's good enough!

I"m thinking the 20/30# will be better and that the 70# will be too fine. Anyone with info on the slag and its possible use?