CO2 emitter question

I'm working in a sealed room 1000 cu/ft with a tank and reg. we've all see the calculator to bring it up to 1500ppm and know every three hours or so the room should be filled again. These calculations are for no doubt plants at least 9" give or take, my question is when supplying co2 to my little kids is there a percentage i should use, say half strength, quarter?.......any input would be great I don't want the co2 to accumulate to toxic levels if they only use a very small amount compared to a few weeks in.

thanks everyone, you're so wise