Ok. Can you give us the ammonia, nitrite, and nitrite levels of the bowl? If you don't have a test kit you can go to a LFS and bring a sample of water, ask them to test it and write down results. Sometimes it costs money(inexpensive though)but sometimes it's free. Also a water change every 2 weeks isn't enough if there's no filter. If the tank isn't cycled, you'd need maybe 50% water change every 2 days. The tank is probably cycled already since it's been 3 years but maybe not because you have no filter.
and that has never happened before