For the last two years, right when I switch from burning our wood stove to radiant oil heat, I have a large die off of coral. The coral loses color, looks terrible then algae takes over parts of the coral. When this occurred in the past, I have changed water, blamed it on heaters, blamed it on everything under the sun. This year I have been monitoring everything with my APEX and have done weekly water tests. I am wondering why this would be occurring. Could it be a PH issue due to dissolved oxygen? That is the only thing that I am not testing (PH). Could the wood stove starve the tank of oxygen, drop the PH, and then when it is shut down the Oxygen returns, drives up the PH and cause the die off? This occurred with my 60 gallon reef in previous years. This year I upgraded to a 175 and it happened again. My parameters have been rock solid (Alk 9.5-10, Calc 420-440, Mag 1350, Nitrate 2-5ppm, Phosphorus 0.03ppm) My salinity did drift from 35 to 37 but that was over time and corrected back to 35. My temp has been stable between 77.5 and 78. My ATO is configured to top off 4 times a day and never runs dry. The whole system is controlled by APEX. I’m baffled!