A-Rod feels like the sixth 'Gronk' brother after investing in Chris Gronkowski's 'Shark Tank' business

ABC | Michael Desmond | Getty Images

The Gronkowski family loves to compete.

All five brothers have had successful careers in professional sports: Rob, Chris, Glenn and Dan played in the NFL, while Gordon played Major League Baseball. Rob, 28, famously nicknamed "The Gronk," is playing in the Super Bowl on Sunday with the New England Patriots.

But these days Chris Gronkowski, 30, is focusing on business, not football. In October, Chris, who most recently played for the Denver Broncos, pitched his company, Ice Shaker, on ABC's "Shark Tank" and brought his siblings along for support. But this time it wasn't the brothers competing — it was the sharks.

All five "Shark Tank" investors, including guest judge, Alex Rodriguez, clamored for a piece of the business, which sells insulated bottles that are an upscale version of plastic cups used to mix up protein shakes.

Rodriguez landed the deal in partnership with Mark Cuban, and the pair invested a combined $150,000 for a 15 percent stake in the business.

For Rodriguez, investing in Chris has been a success.

"He's been terrific," Rodriguez tells CNBC Make It. "He's under promised and he's over delivered. Our sales have done incredibly well."

Alex Rodriguez at eMerge Americas conference in Miami on June 13, 2017.
David A. Grogan | CNBC
Alex Rodriguez at eMerge Americas conference in Miami on June 13, 2017.

Rodriguez even says the deal has made him and Cuban feel like part of the Gronkowski family.

"They have five brothers, [Cuban and I] think now we're like seven brothers having this great company, and we're having a great time," Rodriguez. "Hopefully, sometime in the next few years we have a nice exit."

Gronkowski came on the show seeking $100,000 for 10 percent stake in Ice Shaker. He first had the idea for the business when he noticed that his cabinet full of plastic shaker bottles had problems: They leaked, didn't stay cold and started to smell bad from use. So, he created a stainless steel version.

In its first six months, the business sold about $80,000 worth of shakers, selling online, through Amazon and a few retailers, Gronkowski said on "Shark Tank."

The day the episode aired, Ice Shaker saw record sales.

"We sold out on Amazon within 20 minutes," Gronkowski tells CNBC Make It. "I wish we'd had more in stock there, but at the time we didn't.

"It's been life changing really," he continues.

And, it wasn't just that day. Gronkowski says the sales remained elevated from the publicity of the show for weeks to come. "So many people are not watching and recording the show, and they're watching on other [platforms] like Hulu and stuff like that, where they then see the show later," he explains.

The business has expanded from offering just one product — a $29.99 stainless steel 26 oz. shaker — to offering multiple colors, and a line of "skinny" 20 oz. steel tumblers for drinking smaller quantities, which sell for $19.99.

While you might imagine high profile investors like Rodriguez and Cuban have packed schedules, Gronkowski says both have been helpful and attentive with growing the business.

"Whenever I need to reach out, or just [for] a weekly update, I just shoot them an email and I have a response within 15 minutes," Gronkowski says. "[With] any major concerns I just reach out to them, and get their expert opinion. They've been doing it for so long, especially Mark's team."

For Gronkowski, "Shark Tank" was about finding a business partner instead of just a loan.

"I don't exactly need the money. If I needed just $100,000 I could probably call someone I know, and he would probably give it to me," Gronkowski said on "Shark Tank," with a glance at his famous brother Rob, who landed a $54 million, six-year contract with the Patriots in 2012. "But I need the expertise."

So far, doing business with two sharks has paid off.

"I'm full-time with Ice Shaker now," Gronkowski says. "It's been cranking. I hired my first employee in January, so it's a two man squad right now."

Don't miss: Why Barbara Corcoran invested $50,000 in a new kind of fidget spinner on 'Shark Tank'

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Disclaimer: CNBC owns the exclusive off-network cable rights to "Shark Tank," and NBC Sports is televising Sunday's Super Bowl.

This is an updated version of a previously published story. It has been revised to corrected the terms of Rob Gronkowski's contract.