Yes, the last frontier.....humidity......

How many days are we talking.......last wednesday was res change? And have you been adding water during that time to "top off"? As those beasts get bigger and bigger they are only going to get bigger appetites. If the numbers are staying about the same (raising or lowering about 50ppm a day) you can just add nutes at the same strength when you top off......or slightly less strong if the numbers have risen. They will drink quite a bit of water from here on in as well. Don't let your res get too low as that will REALLY screw with your ratios.

If you add a heater you will see the ppms rise more than if you didn't have extra heat in with them. This is normal but you should keep a good eye on your daily trends.