Inorganic top cover

I'm looking for something to use as top cover other than mulch on top of my smart pots and not a cover crop. Something like say a marble sized or 1/2"-3/4" product that I can easily recover and reuse when I dump pots after grow. Something that won't sink into the soil over the course of a grow and will allow easy watering and top dressing of kelp, EWC etc during the grow yet still help hold moisture. Suggestions?

Clay pebbles?

Why

Ping pong balls

Considered that. Still an option but looking for something with a bit smaller diameter.

I use Perlite because it floats and will not sink when watered.
An inch of Perlite keeps bugs that lay eggs in moist soil at bay to the tune of 80% fewer larvae in the drain screen.
The unwashed Perlite comes in diameters ranging from 1/8" to 1/4" and is my favorite. Perlite also comes powdered to mix with dense soils, or, at the other end, large washed Perlite pebbles at 3/8". I do not use the big ones as the bugs can crawl through the gaps.
Perlite is added as soon as the roots reach the edges of the container, one to three weeks on average, waiting longer allows the bugs to establish homes and neighborhoods.

The reflective white surface reflects the light back to the lower plant, this reduces the trunk stretch a minor amount and adds a bit of bushiness.

An old thread asked about using Perlite alone as a growing medium so I included a photo of a half Perlite and half Rockwool root growth from a single container. About as side by side as it gets and Rockwool kicked ass.