Officials said it wasn't food or a gas in the air, so they're taking a close look at the chemicals.
There were 19 kids who went to the hospital Friday -- sickened from something while at Rose Park pool.
An ambulance took three of the kids to a hospital, while a CityLink bus transported the others.
"We're taking a look at whether it was chemicals or by food intake," said Roberto Aguirre, President of the YMCA.
Monday, Aguirre said they may have pinpointed the root of the illness.
"All the indications right now are that it was chemical, so we're trying to find out why a burst of chemical got into the pool," Aguirre said.
The city said chlorine is not used to treat the water. The President of Willis Supply Company, who used to supply the city, backed that up.
Instead, Darrell Knight said the pools use a chemical called sodium hypochlorite to sanitize the water.
"If the pool just happened to be super chlorinated, the only thing that might happen is that if someone had bleached out hair -- it might turn it a little green," Knight said.
Despite the drama Friday, the pool was back open the very next day -- much to the shock of some parents.
Knight said if a pool is contaminated, a super hypochlorination will be conducted.
"It takes about six hours and at that point, it has killed every piece of bacteria and the pool is safe to get back in," Knight explained.
Mark Young of the Boys & Girls Club, whose kids were on a field trip to Rose Park on Friday, said they are exploring every avenue.
"Is there something in common with the kids? Did they get something from the concession stand or are they hypersensitive to a chemical?" Young said. "We don't know."
Which leaves us with just one likely conclusion.
"Could it be hysteria? Sure," said Young. "I think teachers will tell you, you have one child throw up in a room and it is amazing how many other kids will throw up."
Even so, the investigation into exactly what caused even one kid to get sick continues.
Typically, the pool water is tested every two hours, but since the incident, it's being tested every single hour.