Nicherin (10), at 5-2, won Thursday's fourth race at Gulfstream to start the Rainbow 6.
The carryover coming in was $178,536. Bettors added $116,997 to the Rainbow 6 pool.
Gulfstream has guaranteed that the jackpot pool will be at least $350,000 if there is just one ticket with all six winners in the Rainbow 6.
If that happens, Gulfstream will need to add about $55,000 to the pool.