Lately, the temperature is heading north and I notice that the water that I have in the bubble counter is depleting due to evaporation. I read that I can replace water with mineral oil so as not to keep topping up the water. Besides being a chore, I am more concern about the rubber o ring in my brass bubble counter. I am afraid it will fail if I close it too tight and the higher the frequency I open, the higher chance it might lead due to mishandling.

Anyone is using mineral oil, rather than water? Where can I get them? Is there anything I need to take note if I use that? Will there be tendency that it overflow and goes into the tank water?