In addition to formaldehyde jelly turns green because the catalyst in the jelly reacts with formaldehyde in the air, which leads to the discoloration of the jelly. This change can explain the high formaldehyde content in indoor air.

But if in addition to formaldehyde jelly has turned green, it means that it has absorbed enough formaldehyde and may need to be replaced. Therefore, if it is found that in addition to formaldehyde jelly turns green, it is suggested to replace it with new in addition to formaldehyde jelly to keep the indoor air clean and healthy.