get the chrome grid without the plastic coating

More importantly, check for recurring black gunk between your undermounted sink and the bottom of your stone. If you have it, your sink is leaking and must be reinstalled; that's the only cure.

Get rid of the grid entirely. I got tired of cleaning my all-metal grid - while it didn't get mold, it did get crud in the little corners. I am fine without the grid.

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Look on-line for a solid stainless steel grid that fits your sink. It will probably cost about 4 X more initially than the ones you have been using but will last a lifetime and will not mold out on you.

it still gets crud stuck to it and mold on sink under it. it’s a pain to clean.