My bathroom has been acting funny for some time. Water would not stop running from the fill valve initially. I noticed the old fill valve had a bended holder arm, so the float couldn't stay flat. I thought it was a fill valve problem, so I replaced the fill valve. After the replacement, water still runs into the water tank about every 5 mins, which is arguably better than before. Last night, I put food coloring in the water, and turned off the valve. This morning, the water in the tank is almost all gone, and the water in the toilet bowl is red, meaning water went from the tank to the bowl somehow.
I don't see any visible water flow that goes into the bowl. I'm wondering if I should definitely change the flapper, or if there is anything else I should check first.