Jeff Grolig has really, really good days, and really, really bad ones. That's one thing about being in business for yourself: You have to learn to manage the ups and downs.

Two weeks ago, Grolig was very up. His seafood and gourmet food shop in Potomac was rolling. The day before Thanksgiving, his store had done huge numbers -- three or four times the sales of a typical weekday.

"Oh, it's going great," he said at the time. "We're beating our numbers. We're really doing better than we even thought. We're already thinking about expanding."

Now, sitting at the counter at the Starbucks across from his store, RiverFalls Seafood Co., Grolig sounds rather different. Yesterday it was gray and chilly and misty, and sales were dismal, about 40 percent below normal. So this it not a good time to ask him about his expansion plans.

"It was so off, it was like, something must be wrong," he says, staring at the entrance to his shop. "I couldn't sleep last night. It's been bothering me all morning."

He'd like to blame the weather. But at the fish market early in the morning, everyone said business has been slow there, too. "That made me feel a little better," Grolig says.

But not all better. He goes on:

"We're only in this five months, and there's no pattern. You never know when it's going to be busy, and you can't explain why it's slow, so you start thinking the worst things. You do your best and you realize that you're going to have to throw food away. The food business is so stressful."

Now he really does feel better -- he just needed a little catharsis. Before long, he's talking about Christmas: RiverFalls already has more special orders for Christmas and New Year's than it did for Thanksgiving.

"It's getting to the point that we're getting a little nervous about it," Grolig says, and laughs. But he wouldn't consider putting the brakes on new orders.

"Stop? No, we won't stop taking orders. We'll work three days around the clock if we have to to get it all done."

Grolig is 32. He's excited. He has always wanted to open his own business, and after 14 years working at Sutton Place Gourmet, including 11 years as the chain's seafood buyer, he thought that a little upscale seafood shop, with a variety of prepared foods, would work.

On a typical weekday, RiverFalls takes in about $2,000 to $2,400 dollars, and usually breaks $3,000 on weekend days. The store is on target to do about $800,000 after a year in business, a little more than Grolig had predicted. At that level, the company can pay all its bills, its salaries and its loans. Any more than $800,000, he says, will be profit that can be plowed back into the business.

But Grolig was not right about everything; he miscalculated the division of sales between fresh fish and prepared food. He figured 70 percent of his sales would be fish, a business he knows intimately, and about 30 percent would be prepared food, dishes made by Grolig's equally energetic chef, Ian Rickerby.

As it turns out, the sales split about 50-50. That's put a little strain on RiverFalls' small kitchen, but it's not such a bad thing, either, since prepared food is more profitable.

Throughout the food industry, the sales of prepared food are soaring, and businesses are popping up trying to serve ready-made meals to busy working families. And having seen the fervor with which people come in and buy racks of ribs or even the most expensive dishes, such as fresh lobster meat for $29.99 a pound, Grolig wants to do more.

Get him after a good day, and his dreams are flowing.

"There's a niche out there that we're touching on . . ." he says, and stops to think for a moment. "I'm so torn on it. Do I want to have three retail stores? Do I want to have a retail store and a restaurant? I don't know."

If someone offered him the right space to open a restaurant, he might do that. If someone offered him another 1,500-square-foot store in McLean, which has no room for seats, he would probably replicate his current formula. If he found the perfect 20,000-square-feet spot, he might go much larger, with a combination market and restaurant.

Grolig's desire to branch out is irrepressible, even if he realizes all this dreaming is a little premature. For one thing, his main financial backer -- his father-in-law -- would want to see some profit before expanding, he says. And Grolig wants to be able to compare monthly sales from the previous year so he can get a firmer handle on sales trends.

But thinking out a few years, Grolig has a clear vision of running a little food empire, "like the guy who runs Clyde's Restaurant Group," he says, referring to John Laytham, one of the co-owners of Clyde's. That company has 10 restaurants around town -- six Clyde's, plus 1789 and the Tombs in Georgetown, the Old Ebbitt Grill downtown and Tomato Palace in Columbia.

"It's not too big but it's a real company. He's very diversified," Grolig says. "I picture maybe six or seven different locations, with our corporate offices over one of our stores."

Even Rickerby, the 23-year-old chef, is in on this dream. "I want to be vice president," he says.

It is tempting, of course, to think big when things are going well. It is also dangerous.

"A guy like Jeff, I think one of his challenges will be -- not making a success of his business, because I think he will -- but managing his growth so that he keeps his life in balance and enjoys what he does without being too consumed by it," said Mark Berey, the former president of Sutton Place Gourmet and now the chief financial officer of Giant Food. "There are a lot of people who can make a lot of money with one or two or three stores, but feel compelled to have 10 stores and end up going broke."

At the moment, managing life is a struggle for Grolig, who is married and has a daughter, almost 3. He has taken off a total of five or six days in the last five months.

Berey thinks Grolig will figure it out. "He's young and full of energy, but there's a little part of him that throws the throttle down and says, `Let's don't go crazy here.' "

Then again, Grolig has done crazy things in business before, like asking the owner of Sutton Place Gourmet, Jeff Cohen, if he could be the seafood buyer for the whole company -- when he was only 17.

"Jeff Cohen was probably the most intimidating person I've ever seen in my life," Grolig recalls. "He's in this big leather chair. Oh, God, I was so nervous. So I go in there, and I say I want to be the buyer for the whole company. And he just stares at me."

But Cohen didn't say no. Instead, he asked Grolig if he would work 75 hours a week, with one day off. And Grolig agreed.

"Then he turns to one of his assistants and says, `Is he old enough to drive one of the company trucks?' " Grolig said. "And I wasn't. I had to wait until I was 18."