High nitrates in my tank

[sfuller1963]

i have had a problim with nitrates my tank has been set up for some time with no problems at all and over night the nitrates went off the charts its a 2ft fresh water tank and i cant understand why this has happened as nothing has changed in the tank

 

[sfuller1963]

i have stabaleised it now but wanted to no how this could of happened the bactiria in tank is ok and everything was perfect it just seem to happen quick but for wat reason as nothing in the tank has changed

 

[sfuller1963]

nitrates

i was wondering if anyone new how nitrates would go off the scall in a mater of days tank been set up for a wile now and been running fine. with no problems and just seem to go high nothing has been changed in my tank at all