Hydrofarms have very poor accuracy I have tested 7 now not one actually was correct. DO NOT TRUST the reading on the hydrofarm to be correct. I have found they shift one degree over the set point and 2 under it.

The hydrofarm should be ok on a rack but I put the question to you. You have 4 or 5 animals you are invested in and care about in the rack? Why not invest in a better more reliable accurate t-stat?