I'm in Maine and we are starting to see lows 40 F overnight. My GH keeps air at approximately 55-60 F (it is generally 10-15 F higher than outside temps). My 300 gallon tank is sunk/surrounded by 18" stone dust (16 yards total with a hybrid SHCS). Water temp has not (yet) fallen below 65 F.
My ammonia has been high since I added more fish a week ago and besides (probably) overloading my bacteria I am wondering if there are preferred temperatures parameters for nitrification. I have read that below 60 F diminishes efficacy (but then wondering if that is air, water, or a combination thereof).