Ice melting in a box has the water coming off it at a temp just above freezing until all the ice is gone. Are all phase change materials pretty much the same, with their immediate containment container exterior staying pretty much just above their phase change temp until all the PCM inside has melted? Or, are there additional considerations with PCM, like that it does not conduct internally as well and thus needs to be in flat thinner panels rather than just a big barrel of it? I'm asking because I'll have a 65 gallon tank of hydroponic nutrient solution inside a very well insulated box (4" freezer panels) starting off at an ideal temp of 60F degrees. The nutrient fluid comes and goes via pipes and is cooled back down to a little less than 60F before returning to keep tank contents at 60F. I have just enough room in that box for another identical 65 gallon tank that could be filled with a phase change material to buffer temp inside box in case I ever had exterior temps exceed my ability to chill returning fluid sufficiently. That excess heat would be from both externally rising ambient temps conducting into the box and also the fluid coming back into box much hotter than usual, too. Would the best strategy be to have the 65 gallons of PCM, located in box next to nutrient 65 gallon tank, be designed to melt and absorb heat at, lets say, 61F, thus tempering and slowing down additional excess heat gain in nutrient tank during those extra hot periods that exceeded my usual ability to keep a cap on nutrient tank temps rising via my chilling incoming fluid? What am I missing here or additional considerations to address to maximize efficiency of PCM helping maintain desired 60F temp? Thank you for any comments.