The water level should be about a half inch below the top of the fill tube. To adjust the tank's water level, first adjust the fill valve. This is done by moving the float that's attached to the valve in the direction you want the water level to go, so raising it raises water levels and vice versa.
Toilet Bowl Test: Check bowl water level by flushing toilet. If bowl appears to be full but continues to fill, the valve may be overfilling the bowl causing excess .
When all is well, the water level in your toilet bowl is regulated by the level in the tank and toilet's internal S-trap. When the suction that empties the bowl during a .
If the water level is too low, it will cause the toilet to flush poorly. To adjust your toilet tank water level: If your toilet has a float arm, use the adjustment screw on top of the fill valve to raise or lower the float arm.
I've googled it, and never found an answer beyond a crack in toilet. I dont think thats the case, because its an upstairs toilet and there's no kind .