Why does the color indicator (bromthymol blue) in carbonated water turn from yellow to blue after heating

I can't figure this out for my lab report. So, there were 2 beakers of carbonated water and bromthymol blue was added to both and they were both yellow. Then one beaker was heated until boiling point and it changed color to blue. Why?????????

bromothymol blue is an acid base indicator, It is yellow in acidic solution and blue in basic solution .
Therefore, carbonated water was acidic to start with (7.6

H+ + HCO3- (acidic pH) with heating --> H2O +CO2 (some CO2 dissolved, making pH basic )

Bromothymol blue is yellow in weak acidic solution and blue in weak basic solution. Carbonated water is made by dissolving CO2 in water - the resulting solution is carbonic acid H2CO3, a weak acid which turns the bromothymol blue yellow.
When carbonated water is heated, the CO2 comes out of solution and is lost to the atmosphere, hence the bromothymol blue reverts to blue.