I have found play sand is too light to be used in tanks that have fish large enough to stir it up.
When stirred up, the sand can get sucked into filters and into impeller shafts of pumps (filters) and as the impellers turn grind up volutes, housings and the impellers themselves.
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Above an impeller worn away by sand I used before I realized the damage fine sand can do.
Pool filter sand is graded to be heavy enough to settle after a back wash, so less chance it will get randomly sucked into filters.
So getting a quality Pool Filter sand is important.
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above the space where the impeller works.
I know it hard to see, but there is a figure 8 carved into the housing of this 500 gph pump.
As sand wore away the impeller, it began to wobble, so the sand and wobble carved out the figure 8 rendering the pump unusable.
Of course it didn't happen overnight, but the wear probably shortened the life of the pump by couple years.
I could get decent quality (and cleaner) PFS at places that provide pool supplies, or even shipped.
