Ok, 8 months, nothing has changed. The only thing that pops into mind is, how often do you do a complete breakdown and clean? This should be done every couple months, disenfect everything, boiling water with bleach& dry evetything out.
There's no hybernation with whites, but their own toxins can build up in the tank. Repace moss ever month(unless it's grown) even this can make your frog sick as it stars to decompose.

Does this sound like a good guess?