Epson WP4530 Ink Levels Display Question

In addition to the 4 ink colors, I see a 5th level that's displayed off to the side when I bring up the ink levels check (either on my computer or on the printer's LCD display). I can't find this documented anywhere.

I called Epson Support and the guy I spoke with seemed clueless. Finally, he said something about "maintenance level" but couldn't offer an explanation as to what this is. The printer is 1-day old and all 4 ink levels are at max. This 5th level indicator is at about 3/4 full.

Anyone here know what this is showing?

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Joel
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